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 $215.36   13.453%   $244.3324   $244.33   $244.35   $244.30  
  Purchase #2 $59.53   4.617%   $62.2785   $62.28   $62.30   $62.30  
  Purchase #3 $136.99   5.638%   $144.7135   $144.71   $144.70   $144.70  
  Purchase #4 $121.96   9.170%   $133.1437   $133.14   $133.15   $133.10  
  Purchase #5 $102.79   5.311%   $108.2492   $108.25   $108.25   $108.20  
  Purchase #6 $249.98   7.501%   $268.731   $268.73   $268.75   $268.70  
  Purchase #7 $92.91   10.664%   $102.8179   $102.82   $102.80   $102.80  
  7 purchase totals = $979.52       $1,064.2662   $1,064.26   $1,064.30   $1,064.10