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 $47.71   10.438%   $52.69   $52.69   $52.70   $52.70  
  Purchase #2 $122.45   8.214%   $132.508   $132.51   $132.50   $132.50  
  Purchase #3 $87.79   10.561%   $97.0615   $97.06   $97.05   $97.10  
  Purchase #4 $163.95   12.567%   $184.5536   $184.55   $184.55   $184.60  
  Purchase #5 $49.69   4.473%   $51.9126   $51.91   $51.90   $51.90  
  Purchase #6 $239.43   7.521%   $257.4375   $257.44   $257.45   $257.40  
  Purchase #7 $89.39   8.549%   $97.032   $97.03   $97.05   $97.00  
  7 purchase totals = $800.41       $873.1952   $873.19   $873.20   $873.20