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 $236.87   11.140%   $263.2573   $263.26   $263.25   $263.30  
  Purchase #2 $53.69   9.445%   $58.761   $58.76   $58.75   $58.80  
  Purchase #3 $22.56   10.475%   $24.9232   $24.92   $24.90   $24.90  
  Purchase #4 $96.77   7.442%   $103.9716   $103.97   $103.95   $104.00  
  Purchase #5 $205.90   10.383%   $227.2786   $227.28   $227.30   $227.30  
  Purchase #6 $208.28   5.304%   $219.3272   $219.33   $219.35   $219.30  
  Purchase #7 $77.88   13.647%   $88.5083   $88.51   $88.50   $88.50  
  7 purchase totals = $901.95       $986.0272   $986.03   $986.00   $986.10