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 $88.92   8.536%   $96.5102   $96.51   $96.50   $96.50  
  Purchase #2 $249.57   6.199%   $265.0408   $265.04   $265.05   $265.00  
  Purchase #3 $177.81   9.424%   $194.5668   $194.57   $194.55   $194.60  
  Purchase #4 $237.66   10.222%   $261.9536   $261.95   $261.95   $262.00  
  Purchase #5 $17.54   10.463%   $19.3752   $19.38   $19.40   $19.40  
  Purchase #6 $48.53   4.744%   $50.8323   $50.83   $50.85   $50.80  
  Purchase #7 $177.34   8.679%   $192.7313   $192.73   $192.75   $192.70  
  7 purchase totals = $997.37       $1,081.0102   $1,081.01   $1,081.05   $1,081.00