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 $199.96   13.297%   $226.5487   $226.55   $226.55   $226.50  
  Purchase #2 $33.62   6.847%   $35.922   $35.92   $35.90   $35.90  
  Purchase #3 $86.69   12.529%   $97.5514   $97.55   $97.55   $97.60  
  Purchase #4 $167.78   10.809%   $185.9153   $185.92   $185.90   $185.90  
  Purchase #5 $22.86   3.819%   $23.733   $23.73   $23.75   $23.70  
  Purchase #6 $243.44   10.308%   $268.5338   $268.53   $268.55   $268.50  
  Purchase #7 $66.31   13.665%   $75.3713   $75.37   $75.35   $75.40  
  7 purchase totals = $820.66       $913.5755   $913.57   $913.55   $913.50