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 $169.69   13.504%   $192.6049   $192.60   $192.60   $192.60  
  Purchase #2 $11.37   4.746%   $11.9096   $11.91   $11.90   $11.90  
  Purchase #3 $91.33   7.301%   $97.998   $98.00   $98.00   $98.00  
  Purchase #4 $199.49   12.116%   $223.6602   $223.66   $223.65   $223.70  
  Purchase #5 $42.62   5.390%   $44.9172   $44.92   $44.90   $44.90  
  Purchase #6 $152.61   4.358%   $159.2607   $159.26   $159.25   $159.30  
  Purchase #7 $224.37   9.159%   $244.92   $244.92   $244.90   $244.90  
  7 purchase totals = $891.48       $975.2706   $975.27   $975.20   $975.30