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 $67.28   13.614%   $76.4395   $76.44   $76.45   $76.40  
  Purchase #2 $191.53   5.854%   $202.7422   $202.74   $202.75   $202.70  
  Purchase #3 $88.37   13.276%   $100.102   $100.10   $100.10   $100.10  
  Purchase #4 $125.38   12.692%   $141.2932   $141.29   $141.30   $141.30  
  Purchase #5 $200.74   10.560%   $221.9381   $221.94   $221.95   $221.90  
  Purchase #6 $179.94   8.838%   $195.8431   $195.84   $195.85   $195.80  
  Purchase #7 $168.66   13.412%   $191.2807   $191.28   $191.30   $191.30  
  7 purchase totals = $1,021.90       $1,129.6388   $1,129.63   $1,129.70   $1,129.50