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 $218.31   8.414%   $236.6786   $236.68   $236.70   $236.70  
  Purchase #2 $150.93   7.141%   $161.7079   $161.71   $161.70   $161.70  
  Purchase #3 $179.94   10.595%   $199.0046   $199.00   $199.00   $199.00  
  Purchase #4 $246.69   8.308%   $267.185   $267.19   $267.20   $267.20  
  Purchase #5 $41.86   11.558%   $46.6982   $46.70   $46.70   $46.70  
  Purchase #6 $112.32   11.802%   $125.576   $125.58   $125.60   $125.60  
  Purchase #7 $46.73   10.113%   $51.4558   $51.46   $51.45   $51.50  
  7 purchase totals = $996.78       $1,088.3061   $1,088.32   $1,088.35   $1,088.40