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 $113.59   7.546%   $122.1615   $122.16   $122.15   $122.20  
  Purchase #2 $121.92   9.510%   $133.5146   $133.51   $133.50   $133.50  
  Purchase #3 $109.69   5.150%   $115.339   $115.34   $115.35   $115.30  
  Purchase #4 $240.75   6.307%   $255.9341   $255.93   $255.95   $255.90  
  Purchase #5 $47.28   7.614%   $50.8799   $50.88   $50.90   $50.90  
  Purchase #6 $226.98   11.847%   $253.8703   $253.87   $253.85   $253.90  
  Purchase #7 $26.60   5.103%   $27.9574   $27.96   $27.95   $28.00  
  7 purchase totals = $886.81       $959.6568   $959.65   $959.65   $959.70