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 $116.27   13.755%   $132.2629   $132.26   $132.25   $132.30  
  Purchase #2 $57.73   11.125%   $64.1525   $64.15   $64.15   $64.20  
  Purchase #3 $133.73   7.364%   $143.5779   $143.58   $143.60   $143.60  
  Purchase #4 $72.77   13.209%   $82.3822   $82.38   $82.40   $82.40  
  Purchase #5 $199.25   8.663%   $216.511   $216.51   $216.50   $216.50  
  Purchase #6 $243.97   7.758%   $262.8972   $262.90   $262.90   $262.90  
  Purchase #7 $217.48   3.505%   $225.1027   $225.10   $225.10   $225.10  
  7 purchase totals = $1,041.20       $1,126.8864   $1,126.88   $1,126.90   $1,127.00