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 $245.61   11.822%   $274.646   $274.65   $274.65   $274.60  
  Purchase #2 $62.82   11.778%   $70.2189   $70.22   $70.20   $70.20  
  Purchase #3 $45.82   9.187%   $50.0295   $50.03   $50.05   $50.00  
  Purchase #4 $30.77   3.428%   $31.8248   $31.82   $31.80   $31.80  
  Purchase #5 $43.69   9.311%   $47.758   $47.76   $47.75   $47.80  
  Purchase #6 $101.37   7.718%   $109.1937   $109.19   $109.20   $109.20  
  Purchase #7 $157.33   13.267%   $178.203   $178.20   $178.20   $178.20  
  7 purchase totals = $687.41       $761.8739   $761.87   $761.85   $761.80