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 $205.73   13.874%   $234.273   $234.27   $234.25   $234.30  
  Purchase #2 $123.41   13.839%   $140.4887   $140.49   $140.50   $140.50  
  Purchase #3 $127.35   9.140%   $138.9898   $138.99   $139.00   $139.00  
  Purchase #4 $27.62   5.830%   $29.2302   $29.23   $29.25   $29.20  
  Purchase #5 $46.27   10.809%   $51.2713   $51.27   $51.25   $51.30  
  Purchase #6 $163.80   3.628%   $169.7427   $169.74   $169.75   $169.70  
  Purchase #7 $45.75   3.228%   $47.2268   $47.23   $47.25   $47.20  
  7 purchase totals = $739.93       $811.2225   $811.22   $811.25   $811.20