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 $106.59   12.117%   $119.5055   $119.51   $119.50   $119.50  
  Purchase #2 $104.61   5.482%   $110.3447   $110.34   $110.35   $110.30  
  Purchase #3 $54.80   13.403%   $62.1448   $62.14   $62.15   $62.10  
  Purchase #4 $216.56   13.577%   $245.9624   $245.96   $245.95   $246.00  
  Purchase #5 $163.63   9.478%   $179.1389   $179.14   $179.15   $179.10  
  Purchase #6 $70.84   8.288%   $76.7112   $76.71   $76.70   $76.70  
  Purchase #7 $152.65   8.633%   $165.8283   $165.83   $165.85   $165.80  
  7 purchase totals = $869.68       $959.6358   $959.63   $959.65   $959.50