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 $54.53   13.415%   $61.8452   $61.85   $61.85   $61.80  
  Purchase #2 $188.92   6.201%   $200.6349   $200.63   $200.65   $200.60  
  Purchase #3 $193.48   11.335%   $215.411   $215.41   $215.40   $215.40  
  Purchase #4 $137.89   10.138%   $151.8693   $151.87   $151.85   $151.90  
  Purchase #5 $23.63   10.698%   $26.1579   $26.16   $26.15   $26.20  
  Purchase #6 $53.39   8.759%   $58.0664   $58.07   $58.05   $58.10  
  Purchase #7 $208.72   10.741%   $231.1386   $231.14   $231.15   $231.10  
  7 purchase totals = $860.56       $945.1233   $945.13   $945.10   $945.10