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 $95.86   4.861%   $100.5198   $100.52   $100.50   $100.50  
  Purchase #2 $140.63   10.705%   $155.6844   $155.68   $155.70   $155.70  
  Purchase #3 $154.52   9.720%   $169.5393   $169.54   $169.55   $169.50  
  Purchase #4 $108.58   11.111%   $120.6443   $120.64   $120.65   $120.60  
  Purchase #5 $43.35   9.872%   $47.6295   $47.63   $47.65   $47.60  
  Purchase #6 $33.47   4.362%   $34.93   $34.93   $34.95   $34.90  
  Purchase #7 $119.66   4.744%   $125.3367   $125.34   $125.35   $125.30  
  7 purchase totals = $696.07       $754.2840   $754.28   $754.35   $754.10