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 $85.84   12.281%   $96.382   $96.38   $96.40   $96.40  
  Purchase #2 $161.76   13.109%   $182.9651   $182.97   $182.95   $183.00  
  Purchase #3 $76.84   6.472%   $81.8131   $81.81   $81.80   $81.80  
  Purchase #4 $87.99   4.594%   $92.0323   $92.03   $92.05   $92.00  
  Purchase #5 $188.53   8.386%   $204.3401   $204.34   $204.35   $204.30  
  Purchase #6 $156.25   12.503%   $175.7859   $175.79   $175.80   $175.80  
  Purchase #7 $204.75   4.110%   $213.1652   $213.17   $213.15   $213.20  
  7 purchase totals = $961.96       $1,046.4837   $1,046.49   $1,046.50   $1,046.50