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 $224.69   5.315%   $236.6323   $236.63   $236.65   $236.60  
  Purchase #2 $85.56   7.153%   $91.6801   $91.68   $91.70   $91.70  
  Purchase #3 $99.50   4.824%   $104.2999   $104.30   $104.30   $104.30  
  Purchase #4 $54.47   13.289%   $61.7085   $61.71   $61.70   $61.70  
  Purchase #5 $247.84   6.400%   $263.7018   $263.70   $263.70   $263.70  
  Purchase #6 $6.67   10.369%   $7.3616   $7.36   $7.35   $7.40  
  Purchase #7 $78.78   3.579%   $81.5995   $81.60   $81.60   $81.60  
  7 purchase totals = $797.51       $846.9837   $846.98   $847.00   $847.00