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 $43.94   10.456%   $48.5344   $48.53   $48.55   $48.50  
  Purchase #2 $238.69   13.476%   $270.8559   $270.86   $270.85   $270.90  
  Purchase #3 $208.66   9.179%   $227.8129   $227.81   $227.80   $227.80  
  Purchase #4 $245.25   5.189%   $257.976   $257.98   $258.00   $258.00  
  Purchase #5 $154.79   12.360%   $173.922   $173.92   $173.90   $173.90  
  Purchase #6 $136.51   5.562%   $144.1027   $144.10   $144.10   $144.10  
  Purchase #7 $207.69   4.139%   $216.2863   $216.29   $216.30   $216.30  
  7 purchase totals = $1,235.53       $1,339.4902   $1,339.49   $1,339.50   $1,339.50