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 $93.42   8.772%   $101.6148   $101.61   $101.60   $101.60  
  Purchase #2 $232.72   11.408%   $259.2687   $259.27   $259.25   $259.30  
  Purchase #3 $25.65   4.338%   $26.7627   $26.76   $26.75   $26.80  
  Purchase #4 $169.38   13.785%   $192.729   $192.73   $192.75   $192.70  
  Purchase #5 $150.91   5.821%   $159.6945   $159.69   $159.70   $159.70  
  Purchase #6 $190.36   7.524%   $204.6827   $204.68   $204.70   $204.70  
  Purchase #7 $98.37   5.131%   $103.4174   $103.42   $103.40   $103.40  
  7 purchase totals = $960.81       $1,048.1698   $1,048.16   $1,048.15   $1,048.20