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 $111.54   5.564%   $117.7461   $117.75   $117.75   $117.70  
  Purchase #2 $206.83   4.611%   $216.3669   $216.37   $216.35   $216.40  
  Purchase #3 $66.62   7.169%   $71.396   $71.40   $71.40   $71.40  
  Purchase #4 $133.90   5.617%   $141.4212   $141.42   $141.40   $141.40  
  Purchase #5 $168.68   3.440%   $174.4826   $174.48   $174.50   $174.50  
  Purchase #6 $182.47   10.352%   $201.3593   $201.36   $201.35   $201.40  
  Purchase #7 $16.38   3.263%   $16.9145   $16.91   $16.90   $16.90  
  7 purchase totals = $886.42       $939.6866   $939.69   $939.65   $939.70