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 $217.70   13.571%   $247.2441   $247.24   $247.25   $247.20  
  Purchase #2 $178.62   7.311%   $191.6789   $191.68   $191.70   $191.70  
  Purchase #3 $147.88   10.333%   $163.1604   $163.16   $163.15   $163.20  
  Purchase #4 $187.88   11.114%   $208.761   $208.76   $208.75   $208.80  
  Purchase #5 $161.37   3.866%   $167.6086   $167.61   $167.60   $167.60  
  Purchase #6 $205.44   6.581%   $218.96   $218.96   $218.95   $219.00  
  Purchase #7 $151.27   11.802%   $169.1229   $169.12   $169.10   $169.10  
  7 purchase totals = $1,250.16       $1,366.5359   $1,366.53   $1,366.50   $1,366.60