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 $94.56   11.869%   $105.7833   $105.78   $105.80   $105.80  
  Purchase #2 $31.83   4.267%   $33.1882   $33.19   $33.20   $33.20  
  Purchase #3 $141.99   11.549%   $158.3884   $158.39   $158.40   $158.40  
  Purchase #4 $77.58   7.630%   $83.4994   $83.50   $83.50   $83.50  
  Purchase #5 $244.42   6.747%   $260.911   $260.91   $260.90   $260.90  
  Purchase #6 $190.89   8.446%   $207.0126   $207.01   $207.00   $207.00  
  Purchase #7 $25.97   11.520%   $28.9617   $28.96   $28.95   $29.00  
  7 purchase totals = $807.24       $877.7446   $877.74   $877.75   $877.80