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 $210.92   8.570%   $228.9958   $229.00   $229.00   $229.00  
  Purchase #2 $32.43   9.359%   $35.4651   $35.47   $35.45   $35.50  
  Purchase #3 $25.40   10.512%   $28.07   $28.07   $28.05   $28.10  
  Purchase #4 $151.84   6.290%   $161.3907   $161.39   $161.40   $161.40  
  Purchase #5 $76.87   12.297%   $86.3227   $86.32   $86.30   $86.30  
  Purchase #6 $160.37   8.872%   $174.598   $174.60   $174.60   $174.60  
  Purchase #7 $236.33   10.404%   $260.9178   $260.92   $260.90   $260.90  
  7 purchase totals = $894.16       $975.7601   $975.77   $975.70   $975.80