Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $98.84   12.744%   $111.4362   $111.44   $111.45   $111.40  
  Purchase #2 $228.96   3.427%   $236.8065   $236.81   $236.80   $236.80  
  Purchase #3 $224.56   12.651%   $252.9691   $252.97   $252.95   $253.00  
  Purchase #4 $42.99   5.574%   $45.3863   $45.39   $45.40   $45.40  
  Purchase #5 $211.82   13.750%   $240.9453   $240.95   $240.95   $240.90  
  Purchase #6 $51.95   13.813%   $59.1259   $59.13   $59.15   $59.10  
  Purchase #7 $64.75   5.251%   $68.15   $68.15   $68.15   $68.20  
  7 purchase totals = $923.87       $1,014.8193   $1,014.84   $1,014.85   $1,014.80