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 $47.25   13.247%   $53.5092   $53.51   $53.50   $53.50  
  Purchase #2 $60.25   6.805%   $64.35   $64.35   $64.35   $64.40  
  Purchase #3 $64.47   5.406%   $67.9552   $67.96   $67.95   $68.00  
  Purchase #4 $64.29   9.392%   $70.3281   $70.33   $70.35   $70.30  
  Purchase #5 $170.36   4.413%   $177.878   $177.88   $177.90   $177.90  
  Purchase #6 $32.30   5.126%   $33.9557   $33.96   $33.95   $34.00  
  Purchase #7 $114.48   11.157%   $127.2525   $127.25   $127.25   $127.30  
  7 purchase totals = $553.40       $595.2287   $595.24   $595.25   $595.40