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 $136.43   7.626%   $146.8342   $146.83   $146.85   $146.80  
  Purchase #2 $130.54   5.177%   $137.2981   $137.30   $137.30   $137.30  
  Purchase #3 $65.32   7.707%   $70.3542   $70.35   $70.35   $70.40  
  Purchase #4 $226.48   3.847%   $235.1927   $235.19   $235.20   $235.20  
  Purchase #5 $229.38   13.528%   $260.4105   $260.41   $260.40   $260.40  
  Purchase #6 $155.34   4.509%   $162.3443   $162.34   $162.35   $162.30  
  Purchase #7 $12.26   5.156%   $12.8921   $12.89   $12.90   $12.90  
  7 purchase totals = $955.75       $1,025.3261   $1,025.31   $1,025.35   $1,025.30