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 $53.41   8.869%   $58.1469   $58.15   $58.15   $58.10  
  Purchase #2 $157.59   7.776%   $169.8442   $169.84   $169.85   $169.80  
  Purchase #3 $141.65   12.490%   $159.3421   $159.34   $159.35   $159.30  
  Purchase #4 $139.74   10.346%   $154.1975   $154.20   $154.20   $154.20  
  Purchase #5 $236.49   10.302%   $260.8532   $260.85   $260.85   $260.90  
  Purchase #6 $180.25   10.555%   $199.2754   $199.28   $199.30   $199.30  
  Purchase #7 $232.72   13.790%   $264.8121   $264.81   $264.80   $264.80  
  7 purchase totals = $1,141.85       $1,266.4714   $1,266.47   $1,266.50   $1,266.40