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 $110.93   13.168%   $125.5373   $125.54   $125.55   $125.50  
  Purchase #2 $205.38   5.626%   $216.9347   $216.93   $216.95   $216.90  
  Purchase #3 $151.94   10.465%   $167.8405   $167.84   $167.85   $167.80  
  Purchase #4 $217.99   12.319%   $244.8442   $244.84   $244.85   $244.80  
  Purchase #5 $67.46   12.490%   $75.8858   $75.89   $75.90   $75.90  
  Purchase #6 $126.62   5.468%   $133.5436   $133.54   $133.55   $133.50  
  Purchase #7 $149.49   6.569%   $159.31   $159.31   $159.30   $159.30  
  7 purchase totals = $1,029.81       $1,123.8961   $1,123.89   $1,123.95   $1,123.70