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 $110.89   12.452%   $124.698   $124.70   $124.70   $124.70  
  Purchase #2 $209.38   8.144%   $226.4319   $226.43   $226.45   $226.40  
  Purchase #3 $23.95   6.630%   $25.5379   $25.54   $25.55   $25.50  
  Purchase #4 $81.89   7.697%   $88.1931   $88.19   $88.20   $88.20  
  Purchase #5 $243.77   9.298%   $266.4357   $266.44   $266.45   $266.40  
  Purchase #6 $44.79   6.526%   $47.713   $47.71   $47.70   $47.70  
  Purchase #7 $71.58   7.369%   $76.8547   $76.85   $76.85   $76.90  
  7 purchase totals = $786.25       $855.8643   $855.86   $855.90   $855.80