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 $246.63   3.614%   $255.5432   $255.54   $255.55   $255.50  
  Purchase #2 $55.96   8.202%   $60.5498   $60.55   $60.55   $60.50  
  Purchase #3 $247.86   4.314%   $258.5527   $258.55   $258.55   $258.60  
  Purchase #4 $222.64   9.318%   $243.3856   $243.39   $243.40   $243.40  
  Purchase #5 $224.97   9.438%   $246.2027   $246.20   $246.20   $246.20  
  Purchase #6 $56.81   13.768%   $64.6316   $64.63   $64.65   $64.60  
  Purchase #7 $124.78   9.853%   $137.0746   $137.07   $137.05   $137.10  
  7 purchase totals = $1,179.65       $1,265.9402   $1,265.93   $1,265.95   $1,265.90