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 $219.67   9.462%   $240.4552   $240.46   $240.45   $240.50  
  Purchase #2 $19.83   10.508%   $21.9137   $21.91   $21.90   $21.90  
  Purchase #3 $206.77   7.850%   $223.0014   $223.00   $223.00   $223.00  
  Purchase #4 $168.49   5.322%   $177.457   $177.46   $177.45   $177.50  
  Purchase #5 $49.84   3.171%   $51.4204   $51.42   $51.40   $51.40  
  Purchase #6 $84.34   13.419%   $95.6576   $95.66   $95.65   $95.70  
  Purchase #7 $217.57   11.410%   $242.3947   $242.39   $242.40   $242.40  
  7 purchase totals = $966.51       $1,052.3000   $1,052.30   $1,052.25   $1,052.40