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 $22.91   13.702%   $26.0491   $26.05   $26.05   $26.00  
  Purchase #2 $109.85   10.851%   $121.7698   $121.77   $121.75   $121.80  
  Purchase #3 $165.33   9.222%   $180.5767   $180.58   $180.60   $180.60  
  Purchase #4 $62.98   6.811%   $67.2696   $67.27   $67.25   $67.30  
  Purchase #5 $54.86   5.511%   $57.8833   $57.88   $57.90   $57.90  
  Purchase #6 $182.35   7.165%   $195.4154   $195.42   $195.40   $195.40  
  Purchase #7 $212.72   9.648%   $233.2432   $233.24   $233.25   $233.20  
  7 purchase totals = $811.00       $882.2071   $882.21   $882.20   $882.20