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 $23.93   9.584%   $26.2235   $26.22   $26.20   $26.20  
  Purchase #2 $205.49   9.151%   $224.2944   $224.29   $224.30   $224.30  
  Purchase #3 $118.44   5.162%   $124.5539   $124.55   $124.55   $124.60  
  Purchase #4 $48.40   9.211%   $52.8581   $52.86   $52.85   $52.90  
  Purchase #5 $20.33   5.144%   $21.3758   $21.38   $21.40   $21.40  
  Purchase #6 $62.77   11.463%   $69.9653   $69.97   $69.95   $70.00  
  Purchase #7 $81.83   11.248%   $91.0342   $91.03   $91.05   $91.00  
  7 purchase totals = $561.19       $610.3052   $610.30   $610.30   $610.40