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 $96.39   5.161%   $101.3647   $101.36   $101.35   $101.40  
  Purchase #2 $213.83   10.324%   $235.9058   $235.91   $235.90   $235.90  
  Purchase #3 $115.70   13.396%   $131.1992   $131.20   $131.20   $131.20  
  Purchase #4 $95.76   6.256%   $101.7507   $101.75   $101.75   $101.80  
  Purchase #5 $51.30   13.270%   $58.1075   $58.11   $58.10   $58.10  
  Purchase #6 $209.78   5.764%   $221.8717   $221.87   $221.85   $221.90  
  Purchase #7 $79.91   5.274%   $84.1245   $84.12   $84.10   $84.10  
  7 purchase totals = $862.67       $934.3241   $934.32   $934.25   $934.40