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 $65.57   6.226%   $69.6524   $69.65   $69.65   $69.70  
  Purchase #2 $185.82   11.546%   $207.2748   $207.27   $207.25   $207.30  
  Purchase #3 $124.78   9.440%   $136.5592   $136.56   $136.55   $136.60  
  Purchase #4 $204.76   8.365%   $221.8882   $221.89   $221.90   $221.90  
  Purchase #5 $174.53   13.404%   $197.924   $197.92   $197.90   $197.90  
  Purchase #6 $209.70   8.502%   $227.5287   $227.53   $227.55   $227.50  
  Purchase #7 $226.71   3.485%   $234.6108   $234.61   $234.60   $234.60  
  7 purchase totals = $1,191.87       $1,295.4381   $1,295.43   $1,295.40   $1,295.50