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 $233.63   12.313%   $262.3969   $262.40   $262.40   $262.40  
  Purchase #2 $62.68   7.321%   $67.2688   $67.27   $67.25   $67.30  
  Purchase #3 $40.79   3.633%   $42.2719   $42.27   $42.25   $42.30  
  Purchase #4 $92.63   3.432%   $95.8091   $95.81   $95.80   $95.80  
  Purchase #5 $223.25   10.471%   $246.6265   $246.63   $246.65   $246.60  
  Purchase #6 $122.81   10.844%   $136.1275   $136.13   $136.15   $136.10  
  Purchase #7 $207.52   4.316%   $216.4766   $216.48   $216.50   $216.50  
  7 purchase totals = $983.31       $1,066.9773   $1,066.99   $1,067.00   $1,067.00