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 $141.43   8.634%   $153.6411   $153.64   $153.65   $153.60  
  Purchase #2 $57.59   3.311%   $59.4968   $59.50   $59.50   $59.50  
  Purchase #3 $47.74   5.287%   $50.264   $50.26   $50.25   $50.30  
  Purchase #4 $68.89   6.285%   $73.2197   $73.22   $73.20   $73.20  
  Purchase #5 $169.38   6.766%   $180.8403   $180.84   $180.85   $180.80  
  Purchase #6 $76.72   13.338%   $86.9529   $86.95   $86.95   $87.00  
  Purchase #7 $188.77   8.176%   $204.2038   $204.20   $204.20   $204.20  
  7 purchase totals = $750.52       $808.6186   $808.61   $808.60   $808.60