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 $238.59   3.329%   $246.5327   $246.53   $246.55   $246.50  
  Purchase #2 $11.47   8.597%   $12.4561   $12.46   $12.45   $12.50  
  Purchase #3 $203.88   13.564%   $231.5343   $231.53   $231.55   $231.50  
  Purchase #4 $46.95   3.256%   $48.4787   $48.48   $48.50   $48.50  
  Purchase #5 $218.59   8.198%   $236.51   $236.51   $236.50   $236.50  
  Purchase #6 $217.98   7.504%   $234.3372   $234.34   $234.35   $234.30  
  Purchase #7 $147.77   4.239%   $154.034   $154.03   $154.05   $154.00  
  7 purchase totals = $1,085.23       $1,163.8830   $1,163.88   $1,163.95   $1,163.80