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 $220.68   8.585%   $239.6254   $239.63   $239.65   $239.60  
  Purchase #2 $245.97   4.725%   $257.5921   $257.59   $257.60   $257.60  
  Purchase #3 $47.77   7.442%   $51.325   $51.33   $51.35   $51.30  
  Purchase #4 $216.46   5.866%   $229.1575   $229.16   $229.15   $229.20  
  Purchase #5 $48.84   10.454%   $53.9457   $53.95   $53.95   $53.90  
  Purchase #6 $177.93   10.599%   $196.7888   $196.79   $196.80   $196.80  
  Purchase #7 $88.43   11.119%   $98.2625   $98.26   $98.25   $98.30  
  7 purchase totals = $1,046.08       $1,126.6970   $1,126.71   $1,126.75   $1,126.70