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 $82.90   13.698%   $94.2556   $94.26   $94.25   $94.30  
  Purchase #2 $171.86   12.494%   $193.3322   $193.33   $193.35   $193.30  
  Purchase #3 $148.44   4.622%   $155.3009   $155.30   $155.30   $155.30  
  Purchase #4 $25.93   12.451%   $29.1585   $29.16   $29.15   $29.20  
  Purchase #5 $164.71   5.797%   $174.2582   $174.26   $174.25   $174.30  
  Purchase #6 $105.41   6.791%   $112.5684   $112.57   $112.55   $112.60  
  Purchase #7 $52.83   12.589%   $59.4808   $59.48   $59.50   $59.50  
  7 purchase totals = $752.08       $818.3546   $818.36   $818.35   $818.50