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 $22.41   9.350%   $24.5053   $24.51   $24.50   $24.50  
  Purchase #2 $208.86   7.339%   $224.1882   $224.19   $224.20   $224.20  
  Purchase #3 $141.38   11.500%   $157.6387   $157.64   $157.65   $157.60  
  Purchase #4 $211.76   10.387%   $233.7555   $233.76   $233.75   $233.80  
  Purchase #5 $23.34   5.616%   $24.6508   $24.65   $24.65   $24.70  
  Purchase #6 $201.46   13.308%   $228.2703   $228.27   $228.25   $228.30  
  Purchase #7 $197.45   13.350%   $223.8096   $223.81   $223.80   $223.80  
  7 purchase totals = $1,006.66       $1,116.8184   $1,116.83   $1,116.80   $1,116.90