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 $218.98   9.454%   $239.6824   $239.68   $239.70   $239.70  
  Purchase #2 $69.29   4.626%   $72.4954   $72.50   $72.50   $72.50  
  Purchase #3 $246.38   8.422%   $267.1301   $267.13   $267.15   $267.10  
  Purchase #4 $38.81   7.874%   $41.8659   $41.87   $41.85   $41.90  
  Purchase #5 $108.92   7.694%   $117.3003   $117.30   $117.30   $117.30  
  Purchase #6 $56.71   12.308%   $63.6899   $63.69   $63.70   $63.70  
  Purchase #7 $192.63   3.674%   $199.7072   $199.71   $199.70   $199.70  
  7 purchase totals = $931.72       $1,001.8712   $1,001.88   $1,001.90   $1,001.90