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 $38.27   7.482%   $41.1334   $41.13   $41.15   $41.10  
  Purchase #2 $53.29   13.165%   $60.3056   $60.31   $60.30   $60.30  
  Purchase #3 $136.48   10.656%   $151.0233   $151.02   $151.00   $151.00  
  Purchase #4 $211.36   11.708%   $236.106   $236.11   $236.10   $236.10  
  Purchase #5 $209.89   7.655%   $225.9571   $225.96   $225.95   $226.00  
  Purchase #6 $152.86   3.859%   $158.7589   $158.76   $158.75   $158.80  
  Purchase #7 $122.50   5.470%   $129.2008   $129.20   $129.20   $129.20  
  7 purchase totals = $924.65       $1,002.4851   $1,002.49   $1,002.45   $1,002.50