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 $125.63   8.486%   $136.291   $136.29   $136.30   $136.30  
  Purchase #2 $179.36   4.782%   $187.937   $187.94   $187.95   $187.90  
  Purchase #3 $135.35   4.244%   $141.0943   $141.09   $141.10   $141.10  
  Purchase #4 $183.54   11.677%   $204.972   $204.97   $204.95   $205.00  
  Purchase #5 $150.75   10.623%   $166.7642   $166.76   $166.75   $166.80  
  Purchase #6 $217.54   12.215%   $244.1125   $244.11   $244.10   $244.10  
  Purchase #7 $144.54   10.673%   $159.9668   $159.97   $159.95   $160.00  
  7 purchase totals = $1,136.71       $1,241.1378   $1,241.13   $1,241.10   $1,241.20