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 $48.46   4.731%   $50.7526   $50.75   $50.75   $50.80  
  Purchase #2 $97.37   11.140%   $108.217   $108.22   $108.20   $108.20  
  Purchase #3 $213.43   6.213%   $226.6904   $226.69   $226.70   $226.70  
  Purchase #4 $44.86   10.768%   $49.6905   $49.69   $49.70   $49.70  
  Purchase #5 $202.71   13.569%   $230.2157   $230.22   $230.20   $230.20  
  Purchase #6 $227.29   11.838%   $254.1966   $254.20   $254.20   $254.20  
  Purchase #7 $46.75   5.138%   $49.152   $49.15   $49.15   $49.20  
  7 purchase totals = $880.87       $968.9148   $968.92   $968.90   $969.00