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 $19.74   9.275%   $21.5709   $21.57   $21.55   $21.60  
  Purchase #2 $227.80   7.505%   $244.8964   $244.90   $244.90   $244.90  
  Purchase #3 $205.75   10.418%   $227.185   $227.19   $227.20   $227.20  
  Purchase #4 $96.75   10.476%   $106.8855   $106.89   $106.90   $106.90  
  Purchase #5 $231.50   7.719%   $249.3695   $249.37   $249.35   $249.40  
  Purchase #6 $123.90   11.152%   $137.7173   $137.72   $137.70   $137.70  
  Purchase #7 $133.47   7.406%   $143.3548   $143.35   $143.35   $143.40  
  7 purchase totals = $1,038.91       $1,130.9794   $1,130.99   $1,130.95   $1,131.10