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 $71.82   5.715%   $75.9245   $75.92   $75.90   $75.90  
  Purchase #2 $125.47   10.357%   $138.4649   $138.46   $138.45   $138.50  
  Purchase #3 $112.28   7.508%   $120.71   $120.71   $120.70   $120.70  
  Purchase #4 $136.92   6.182%   $145.3844   $145.38   $145.40   $145.40  
  Purchase #5 $182.70   10.204%   $201.3427   $201.34   $201.35   $201.30  
  Purchase #6 $236.89   10.687%   $262.2064   $262.21   $262.20   $262.20  
  Purchase #7 $105.66   7.460%   $113.5422   $113.54   $113.55   $113.50  
  7 purchase totals = $971.74       $1,057.5751   $1,057.56   $1,057.55   $1,057.50