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 $230.87   13.317%   $261.615   $261.62   $261.60   $261.60  
  Purchase #2 $225.90   4.602%   $236.2959   $236.30   $236.30   $236.30  
  Purchase #3 $111.59   7.495%   $119.9537   $119.95   $119.95   $120.00  
  Purchase #4 $52.87   3.831%   $54.8954   $54.90   $54.90   $54.90  
  Purchase #5 $167.78   4.471%   $175.2814   $175.28   $175.30   $175.30  
  Purchase #6 $173.32   6.745%   $185.0104   $185.01   $185.00   $185.00  
  Purchase #7 $208.66   4.720%   $218.5088   $218.51   $218.50   $218.50  
  7 purchase totals = $1,170.99       $1,251.5606   $1,251.57   $1,251.55   $1,251.60