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 $24.97   5.555%   $26.3571   $26.36   $26.35   $26.40  
  Purchase #2 $225.34   7.617%   $242.5041   $242.50   $242.50   $242.50  
  Purchase #3 $12.32   7.617%   $13.2584   $13.26   $13.25   $13.30  
  Purchase #4 $66.86   3.278%   $69.0517   $69.05   $69.05   $69.10  
  Purchase #5 $249.55   10.829%   $276.5738   $276.57   $276.55   $276.60  
  Purchase #6 $25.33   6.168%   $26.8924   $26.89   $26.90   $26.90  
  Purchase #7 $91.84   7.748%   $98.9558   $98.96   $98.95   $99.00  
  7 purchase totals = $696.21       $753.5933   $753.59   $753.55   $753.80