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 $64.96   5.442%   $68.4951   $68.50   $68.50   $68.50  
  Purchase #2 $162.71   9.583%   $178.3025   $178.30   $178.30   $178.30  
  Purchase #3 $117.35   13.873%   $133.63   $133.63   $133.65   $133.60  
  Purchase #4 $207.65   3.656%   $215.2417   $215.24   $215.25   $215.20  
  Purchase #5 $150.32   9.607%   $164.7612   $164.76   $164.75   $164.80  
  Purchase #6 $102.52   4.562%   $107.197   $107.20   $107.20   $107.20  
  Purchase #7 $90.39   5.809%   $95.6408   $95.64   $95.65   $95.60  
  7 purchase totals = $895.90       $963.2683   $963.27   $963.30   $963.20