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 $244.63   8.491%   $265.4015   $265.40   $265.40   $265.40  
  Purchase #2 $37.80   9.701%   $41.467   $41.47   $41.45   $41.50  
  Purchase #3 $11.82   12.111%   $13.2515   $13.25   $13.25   $13.30  
  Purchase #4 $8.82   8.719%   $9.589   $9.59   $9.60   $9.60  
  Purchase #5 $59.43   13.577%   $67.4988   $67.50   $67.50   $67.50  
  Purchase #6 $192.95   7.740%   $207.8843   $207.88   $207.90   $207.90  
  Purchase #7 $139.78   11.576%   $155.9609   $155.96   $155.95   $156.00  
  7 purchase totals = $695.23       $761.0530   $761.05   $761.05   $761.20