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 $213.89   4.556%   $223.6348   $223.63   $223.65   $223.60  
  Purchase #2 $26.33   13.738%   $29.9472   $29.95   $29.95   $29.90  
  Purchase #3 $205.34   6.348%   $218.375   $218.38   $218.40   $218.40  
  Purchase #4 $231.36   4.167%   $241.0008   $241.00   $241.00   $241.00  
  Purchase #5 $61.93   3.797%   $64.2815   $64.28   $64.30   $64.30  
  Purchase #6 $157.95   4.464%   $165.0009   $165.00   $165.00   $165.00  
  Purchase #7 $7.59   10.677%   $8.4004   $8.40   $8.40   $8.40  
  7 purchase totals = $904.39       $950.6406   $950.64   $950.70   $950.60