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 $82.99   11.739%   $92.7322   $92.73   $92.75   $92.70  
  Purchase #2 $140.89   8.849%   $153.3574   $153.36   $153.35   $153.40  
  Purchase #3 $97.82   8.199%   $105.8403   $105.84   $105.85   $105.80  
  Purchase #4 $46.85   11.337%   $52.1614   $52.16   $52.15   $52.20  
  Purchase #5 $189.65   12.408%   $213.1818   $213.18   $213.20   $213.20  
  Purchase #6 $53.92   3.454%   $55.7824   $55.78   $55.80   $55.80  
  Purchase #7 $146.54   12.341%   $164.6245   $164.62   $164.60   $164.60  
  7 purchase totals = $758.66       $837.6800   $837.67   $837.70   $837.70