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 $38.68   6.828%   $41.3211   $41.32   $41.30   $41.30  
  Purchase #2 $64.86   13.866%   $73.8535   $73.85   $73.85   $73.90  
  Purchase #3 $235.54   13.630%   $267.6441   $267.64   $267.65   $267.60  
  Purchase #4 $42.61   6.532%   $45.3933   $45.39   $45.40   $45.40  
  Purchase #5 $215.88   5.340%   $227.408   $227.41   $227.40   $227.40  
  Purchase #6 $86.68   13.208%   $98.1287   $98.13   $98.15   $98.10  
  Purchase #7 $12.46   10.747%   $13.7991   $13.80   $13.80   $13.80  
  7 purchase totals = $696.71       $767.5478   $767.54   $767.55   $767.50