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 $67.81   12.774%   $76.472   $76.47   $76.45   $76.50  
  Purchase #2 $44.30   5.567%   $46.7662   $46.77   $46.75   $46.80  
  Purchase #3 $242.83   5.544%   $256.2925   $256.29   $256.30   $256.30  
  Purchase #4 $146.30   5.604%   $154.4987   $154.50   $154.50   $154.50  
  Purchase #5 $42.72   12.161%   $47.9152   $47.92   $47.90   $47.90  
  Purchase #6 $227.31   8.679%   $247.0382   $247.04   $247.05   $247.00  
  Purchase #7 $240.72   6.862%   $257.2382   $257.24   $257.25   $257.20  
  7 purchase totals = $1,011.99       $1,086.2210   $1,086.23   $1,086.20   $1,086.20