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 $23.73   6.730%   $25.327   $25.33   $25.35   $25.30  
  Purchase #2 $152.81   8.826%   $166.297   $166.30   $166.30   $166.30  
  Purchase #3 $22.59   3.563%   $23.3949   $23.39   $23.40   $23.40  
  Purchase #4 $77.31   9.239%   $84.4527   $84.45   $84.45   $84.50  
  Purchase #5 $188.45   6.298%   $200.3186   $200.32   $200.30   $200.30  
  Purchase #6 $95.28   3.652%   $98.7596   $98.76   $98.75   $98.80  
  Purchase #7 $120.74   5.638%   $127.5473   $127.55   $127.55   $127.50  
  7 purchase totals = $680.91       $726.0971   $726.10   $726.10   $726.10