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 $132.67   8.371%   $143.7758   $143.78   $143.80   $143.80  
  Purchase #2 $207.92   10.315%   $229.3669   $229.37   $229.35   $229.40  
  Purchase #3 $113.45   8.766%   $123.395   $123.40   $123.40   $123.40  
  Purchase #4 $92.87   5.297%   $97.7893   $97.79   $97.80   $97.80  
  Purchase #5 $143.73   9.866%   $157.9104   $157.91   $157.90   $157.90  
  Purchase #6 $64.80   7.613%   $69.7332   $69.73   $69.75   $69.70  
  Purchase #7 $121.45   6.686%   $129.5701   $129.57   $129.55   $129.60  
  7 purchase totals = $876.89       $951.5407   $951.55   $951.55   $951.60