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 $208.34   13.128%   $235.6909   $235.69   $235.70   $235.70  
  Purchase #2 $10.83   12.118%   $12.1424   $12.14   $12.15   $12.10  
  Purchase #3 $19.62   3.469%   $20.3006   $20.30   $20.30   $20.30  
  Purchase #4 $136.56   3.314%   $141.0856   $141.09   $141.10   $141.10  
  Purchase #5 $148.71   11.823%   $166.292   $166.29   $166.30   $166.30  
  Purchase #6 $57.30   13.185%   $64.855   $64.86   $64.85   $64.90  
  Purchase #7 $249.78   8.583%   $271.2186   $271.22   $271.20   $271.20  
  7 purchase totals = $831.14       $911.5851   $911.59   $911.60   $911.60