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 $217.55   9.236%   $237.6429   $237.64   $237.65   $237.60  
  Purchase #2 $229.62   6.863%   $245.3788   $245.38   $245.40   $245.40  
  Purchase #3 $62.56   7.376%   $67.1744   $67.17   $67.15   $67.20  
  Purchase #4 $232.85   5.714%   $246.155   $246.16   $246.15   $246.20  
  Purchase #5 $178.59   11.494%   $199.1171   $199.12   $199.10   $199.10  
  Purchase #6 $234.91   13.778%   $267.2759   $267.28   $267.30   $267.30  
  Purchase #7 $60.80   9.775%   $66.7432   $66.74   $66.75   $66.70  
  7 purchase totals = $1,216.88       $1,329.4873   $1,329.49   $1,329.50   $1,329.50