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 $97.69   6.874%   $104.4052   $104.41   $104.40   $104.40  
  Purchase #2 $236.45   6.414%   $251.6159   $251.62   $251.60   $251.60  
  Purchase #3 $60.27   7.784%   $64.9614   $64.96   $64.95   $65.00  
  Purchase #4 $71.68   7.658%   $77.1693   $77.17   $77.15   $77.20  
  Purchase #5 $170.69   13.163%   $193.1579   $193.16   $193.15   $193.20  
  Purchase #6 $11.96   11.538%   $13.3399   $13.34   $13.35   $13.30  
  Purchase #7 $96.90   10.475%   $107.0503   $107.05   $107.05   $107.10  
  7 purchase totals = $745.64       $811.6999   $811.71   $811.65   $811.80