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 $92.48   5.513%   $97.5784   $97.58   $97.60   $97.60  
  Purchase #2 $222.40   6.521%   $236.9027   $236.90   $236.90   $236.90  
  Purchase #3 $227.85   11.714%   $254.5403   $254.54   $254.55   $254.50  
  Purchase #4 $106.55   8.809%   $115.936   $115.94   $115.95   $115.90  
  Purchase #5 $126.79   5.214%   $133.4008   $133.40   $133.40   $133.40  
  Purchase #6 $53.86   3.801%   $55.9072   $55.91   $55.90   $55.90  
  Purchase #7 $53.82   6.128%   $57.1181   $57.12   $57.10   $57.10  
  7 purchase totals = $883.75       $951.3835   $951.39   $951.40   $951.30