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 $22.98   13.253%   $26.0255   $26.03   $26.05   $26.00  
  Purchase #2 $169.88   6.294%   $180.5722   $180.57   $180.55   $180.60  
  Purchase #3 $142.86   6.745%   $152.4959   $152.50   $152.50   $152.50  
  Purchase #4 $59.36   13.543%   $67.3991   $67.40   $67.40   $67.40  
  Purchase #5 $101.26   6.808%   $108.1538   $108.15   $108.15   $108.20  
  Purchase #6 $162.98   9.746%   $178.864   $178.86   $178.85   $178.90  
  Purchase #7 $12.49   6.782%   $13.3371   $13.34   $13.35   $13.30  
  7 purchase totals = $671.81       $726.8476   $726.85   $726.85   $726.90