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 $156.95   10.847%   $173.9744   $173.97   $173.95   $174.00  
  Purchase #2 $119.76   11.593%   $133.6438   $133.64   $133.65   $133.60  
  Purchase #3 $166.75   7.292%   $178.9094   $178.91   $178.90   $178.90  
  Purchase #4 $23.96   3.793%   $24.8688   $24.87   $24.85   $24.90  
  Purchase #5 $148.49   13.787%   $168.9623   $168.96   $168.95   $169.00  
  Purchase #6 $93.79   13.721%   $106.6589   $106.66   $106.65   $106.70  
  Purchase #7 $84.69   10.863%   $93.8899   $93.89   $93.90   $93.90  
  7 purchase totals = $794.39       $880.9075   $880.90   $880.85   $881.00