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 $59.46   6.833%   $63.5229   $63.52   $63.50   $63.50  
  Purchase #2 $187.58   9.867%   $206.0885   $206.09   $206.10   $206.10  
  Purchase #3 $193.55   12.725%   $218.1792   $218.18   $218.20   $218.20  
  Purchase #4 $249.60   8.754%   $271.45   $271.45   $271.45   $271.50  
  Purchase #5 $155.38   5.712%   $164.2553   $164.26   $164.25   $164.30  
  Purchase #6 $6.54   4.515%   $6.8353   $6.84   $6.85   $6.80  
  Purchase #7 $20.72   12.758%   $23.3635   $23.36   $23.35   $23.40  
  7 purchase totals = $872.83       $953.6947   $953.70   $953.70   $953.80