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 $146.92   8.376%   $159.226   $159.23   $159.25   $159.20  
  Purchase #2 $90.41   7.635%   $97.3128   $97.31   $97.30   $97.30  
  Purchase #3 $77.28   12.334%   $86.8117   $86.81   $86.80   $86.80  
  Purchase #4 $176.28   9.461%   $192.9579   $192.96   $192.95   $193.00  
  Purchase #5 $192.74   9.463%   $210.979   $210.98   $211.00   $211.00  
  Purchase #6 $156.76   10.590%   $173.3609   $173.36   $173.35   $173.40  
  Purchase #7 $40.86   4.582%   $42.7322   $42.73   $42.75   $42.70  
  7 purchase totals = $881.25       $963.3805   $963.38   $963.40   $963.40