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 $33.58   8.651%   $36.485   $36.49   $36.50   $36.50  
  Purchase #2 $215.88   9.617%   $236.6412   $236.64   $236.65   $236.60  
  Purchase #3 $231.95   4.228%   $241.7568   $241.76   $241.75   $241.80  
  Purchase #4 $113.40   5.230%   $119.3308   $119.33   $119.35   $119.30  
  Purchase #5 $58.78   9.318%   $64.2571   $64.26   $64.25   $64.30  
  Purchase #6 $30.45   7.152%   $32.6278   $32.63   $32.65   $32.60  
  Purchase #7 $32.96   3.694%   $34.1775   $34.18   $34.20   $34.20  
  7 purchase totals = $717.00       $765.2762   $765.29   $765.35   $765.30