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 $33.44   11.317%   $37.2244   $37.22   $37.20   $37.20  
  Purchase #2 $51.92   12.371%   $58.343   $58.34   $58.35   $58.30  
  Purchase #3 $216.82   9.123%   $236.6005   $236.60   $236.60   $236.60  
  Purchase #4 $126.73   10.716%   $140.3104   $140.31   $140.30   $140.30  
  Purchase #5 $131.60   10.324%   $145.1864   $145.19   $145.20   $145.20  
  Purchase #6 $225.38   12.647%   $253.8838   $253.88   $253.90   $253.90  
  Purchase #7 $158.95   6.801%   $169.7602   $169.76   $169.75   $169.80  
  7 purchase totals = $944.84       $1,041.3087   $1,041.30   $1,041.30   $1,041.30