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 $21.95   13.555%   $24.9253   $24.93   $24.95   $24.90  
  Purchase #2 $51.51   10.257%   $56.7934   $56.79   $56.80   $56.80  
  Purchase #3 $145.62   9.125%   $158.9078   $158.91   $158.90   $158.90  
  Purchase #4 $69.92   10.669%   $77.3798   $77.38   $77.40   $77.40  
  Purchase #5 $153.49   5.616%   $162.11   $162.11   $162.10   $162.10  
  Purchase #6 $59.79   8.561%   $64.9086   $64.91   $64.90   $64.90  
  Purchase #7 $22.39   4.122%   $23.3129   $23.31   $23.30   $23.30  
  7 purchase totals = $524.67       $568.3378   $568.34   $568.35   $568.30