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 $151.76   7.118%   $162.5623   $162.56   $162.55   $162.60  
  Purchase #2 $54.43   11.278%   $60.5686   $60.57   $60.55   $60.60  
  Purchase #3 $82.49   12.125%   $92.4919   $92.49   $92.50   $92.50  
  Purchase #4 $202.47   4.399%   $211.3767   $211.38   $211.40   $211.40  
  Purchase #5 $245.48   13.143%   $277.7434   $277.74   $277.75   $277.70  
  Purchase #6 $15.48   5.416%   $16.3184   $16.32   $16.30   $16.30  
  Purchase #7 $33.88   7.749%   $36.5054   $36.51   $36.50   $36.50  
  7 purchase totals = $785.99       $857.5667   $857.57   $857.55   $857.60