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 $246.30   12.157%   $276.2427   $276.24   $276.25   $276.20  
  Purchase #2 $162.76   9.756%   $178.6389   $178.64   $178.65   $178.60  
  Purchase #3 $68.58   5.560%   $72.393   $72.39   $72.40   $72.40  
  Purchase #4 $5.89   3.502%   $6.0963   $6.10   $6.10   $6.10  
  Purchase #5 $176.48   3.501%   $182.6586   $182.66   $182.65   $182.70  
  Purchase #6 $136.53   3.630%   $141.486   $141.49   $141.50   $141.50  
  Purchase #7 $186.98   12.157%   $209.7112   $209.71   $209.70   $209.70  
  7 purchase totals = $983.52       $1,067.2267   $1,067.23   $1,067.25   $1,067.20