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 $117.69   6.619%   $125.4799   $125.48   $125.50   $125.50  
  Purchase #2 $229.25   6.263%   $243.6079   $243.61   $243.60   $243.60  
  Purchase #3 $154.42   11.114%   $171.5822   $171.58   $171.60   $171.60  
  Purchase #4 $203.47   10.204%   $224.2321   $224.23   $224.25   $224.20  
  Purchase #5 $63.42   5.449%   $66.8758   $66.88   $66.90   $66.90  
  Purchase #6 $80.86   6.615%   $86.2089   $86.21   $86.20   $86.20  
  Purchase #7 $68.26   4.245%   $71.1576   $71.16   $71.15   $71.20  
  7 purchase totals = $917.37       $989.1444   $989.15   $989.20   $989.20