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 $195.36   6.756%   $208.5585   $208.56   $208.55   $208.60  
  Purchase #2 $94.87   12.147%   $106.3939   $106.39   $106.40   $106.40  
  Purchase #3 $141.51   3.350%   $146.2506   $146.25   $146.25   $146.30  
  Purchase #4 $51.83   7.332%   $55.6302   $55.63   $55.65   $55.60  
  Purchase #5 $72.87   5.793%   $77.0914   $77.09   $77.10   $77.10  
  Purchase #6 $117.85   12.469%   $132.5447   $132.54   $132.55   $132.50  
  Purchase #7 $200.50   13.104%   $226.7735   $226.77   $226.75   $226.80  
  7 purchase totals = $874.79       $953.2428   $953.23   $953.25   $953.30