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 $174.81   4.428%   $182.5506   $182.55   $182.55   $182.60  
  Purchase #2 $216.38   12.763%   $243.9966   $244.00   $244.00   $244.00  
  Purchase #3 $126.65   3.269%   $130.7902   $130.79   $130.80   $130.80  
  Purchase #4 $81.71   5.312%   $86.0504   $86.05   $86.05   $86.10  
  Purchase #5 $239.78   8.392%   $259.9023   $259.90   $259.90   $259.90  
  Purchase #6 $73.29   3.564%   $75.9021   $75.90   $75.90   $75.90  
  Purchase #7 $232.51   12.522%   $261.6249   $261.62   $261.60   $261.60  
  7 purchase totals = $1,145.13       $1,240.8171   $1,240.81   $1,240.80   $1,240.90