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 $126.67   4.263%   $132.0699   $132.07   $132.05   $132.10  
  Purchase #2 $86.27   3.795%   $89.5439   $89.54   $89.55   $89.50  
  Purchase #3 $201.64   9.825%   $221.4511   $221.45   $221.45   $221.50  
  Purchase #4 $245.95   10.816%   $272.552   $272.55   $272.55   $272.60  
  Purchase #5 $13.62   3.274%   $14.0659   $14.07   $14.05   $14.10  
  Purchase #6 $217.83   8.815%   $237.0317   $237.03   $237.05   $237.00  
  Purchase #7 $69.99   7.545%   $75.2707   $75.27   $75.25   $75.30  
  7 purchase totals = $961.97       $1,041.9852   $1,041.98   $1,041.95   $1,042.10