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 $44.72   4.128%   $46.566   $46.57   $46.55   $46.60  
  Purchase #2 $87.97   12.455%   $98.9267   $98.93   $98.95   $98.90  
  Purchase #3 $47.40   12.356%   $53.2567   $53.26   $53.25   $53.30  
  Purchase #4 $103.93   11.355%   $115.7313   $115.73   $115.75   $115.70  
  Purchase #5 $250.53   10.316%   $276.3747   $276.37   $276.35   $276.40  
  Purchase #6 $24.34   7.465%   $26.157   $26.16   $26.15   $26.20  
  Purchase #7 $125.38   7.542%   $134.8362   $134.84   $134.85   $134.80  
  7 purchase totals = $684.27       $751.8486   $751.86   $751.85   $751.90