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 $59.74   3.848%   $62.0388   $62.04   $62.05   $62.00  
  Purchase #2 $58.50   8.489%   $63.4661   $63.47   $63.45   $63.50  
  Purchase #3 $48.31   7.390%   $51.8801   $51.88   $51.90   $51.90  
  Purchase #4 $24.74   5.723%   $26.1559   $26.16   $26.15   $26.20  
  Purchase #5 $16.31   4.207%   $16.9962   $17.00   $17.00   $17.00  
  Purchase #6 $180.74   11.543%   $201.6028   $201.60   $201.60   $201.60  
  Purchase #7 $53.35   9.460%   $58.3969   $58.40   $58.40   $58.40  
  7 purchase totals = $441.69       $480.5368   $480.55   $480.55   $480.60