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 $240.84   11.670%   $268.946   $268.95   $268.95   $268.90  
  Purchase #2 $164.77   6.223%   $175.0236   $175.02   $175.00   $175.00  
  Purchase #3 $135.66   11.625%   $151.4305   $151.43   $151.45   $151.40  
  Purchase #4 $236.70   3.614%   $245.2543   $245.25   $245.25   $245.30  
  Purchase #5 $239.82   7.632%   $258.1231   $258.12   $258.10   $258.10  
  Purchase #6 $157.45   5.769%   $166.5333   $166.53   $166.55   $166.50  
  Purchase #7 $135.48   7.651%   $145.8456   $145.85   $145.85   $145.80  
  7 purchase totals = $1,310.72       $1,411.1564   $1,411.15   $1,411.15   $1,411.00