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 $217.87   13.812%   $247.9622   $247.96   $247.95   $248.00  
  Purchase #2 $226.85   13.457%   $257.3772   $257.38   $257.40   $257.40  
  Purchase #3 $157.86   4.663%   $165.221   $165.22   $165.20   $165.20  
  Purchase #4 $21.52   12.296%   $24.1661   $24.17   $24.15   $24.20  
  Purchase #5 $241.56   3.240%   $249.3865   $249.39   $249.40   $249.40  
  Purchase #6 $223.80   12.620%   $252.0436   $252.04   $252.05   $252.00  
  Purchase #7 $12.63   5.660%   $13.3449   $13.34   $13.35   $13.30  
  7 purchase totals = $1,102.09       $1,209.5015   $1,209.50   $1,209.50   $1,209.50