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 $206.97   11.764%   $231.318   $231.32   $231.30   $231.30  
  Purchase #2 $182.67   3.283%   $188.6671   $188.67   $188.65   $188.70  
  Purchase #3 $149.80   5.835%   $158.5408   $158.54   $158.55   $158.50  
  Purchase #4 $104.40   10.562%   $115.4267   $115.43   $115.45   $115.40  
  Purchase #5 $249.42   8.361%   $270.274   $270.27   $270.25   $270.30  
  Purchase #6 $186.91   7.468%   $200.8684   $200.87   $200.85   $200.90  
  Purchase #7 $170.25   7.253%   $182.5982   $182.60   $182.60   $182.60  
  7 purchase totals = $1,250.42       $1,347.6932   $1,347.70   $1,347.65   $1,347.70