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 $237.99   4.468%   $248.6234   $248.62   $248.60   $248.60  
  Purchase #2 $205.36   3.497%   $212.5414   $212.54   $212.55   $212.50  
  Purchase #3 $62.88   5.124%   $66.102   $66.10   $66.10   $66.10  
  Purchase #4 $116.51   13.695%   $132.466   $132.47   $132.45   $132.50  
  Purchase #5 $232.69   12.123%   $260.899   $260.90   $260.90   $260.90  
  Purchase #6 $225.43   4.467%   $235.5   $235.50   $235.50   $235.50  
  Purchase #7 $101.28   12.304%   $113.7415   $113.74   $113.75   $113.70  
  7 purchase totals = $1,182.14       $1,269.8733   $1,269.87   $1,269.85   $1,269.80