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 $48.75   11.253%   $54.2358   $54.24   $54.25   $54.20  
  Purchase #2 $229.75   6.277%   $244.1714   $244.17   $244.15   $244.20  
  Purchase #3 $57.50   4.546%   $60.114   $60.11   $60.10   $60.10  
  Purchase #4 $247.26   11.802%   $276.4416   $276.44   $276.45   $276.40  
  Purchase #5 $71.95   6.167%   $76.3872   $76.39   $76.40   $76.40  
  Purchase #6 $170.79   11.263%   $190.0261   $190.03   $190.05   $190.00  
  Purchase #7 $134.92   12.165%   $151.333   $151.33   $151.35   $151.30  
  7 purchase totals = $960.92       $1,052.7091   $1,052.71   $1,052.75   $1,052.60