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 $249.76   7.422%   $268.2972   $268.30   $268.30   $268.30  
  Purchase #2 $18.54   10.317%   $20.4528   $20.45   $20.45   $20.50  
  Purchase #3 $39.86   11.390%   $44.4001   $44.40   $44.40   $44.40  
  Purchase #4 $241.47   10.758%   $267.4473   $267.45   $267.45   $267.40  
  Purchase #5 $17.91   13.180%   $20.2705   $20.27   $20.25   $20.30  
  Purchase #6 $225.53   12.355%   $253.3942   $253.39   $253.40   $253.40  
  Purchase #7 $232.99   3.715%   $241.6456   $241.65   $241.65   $241.60  
  7 purchase totals = $1,026.06       $1,115.9077   $1,115.91   $1,115.90   $1,115.90