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 $46.28   8.752%   $50.3304   $50.33   $50.35   $50.30  
  Purchase #2 $59.63   10.217%   $65.7224   $65.72   $65.70   $65.70  
  Purchase #3 $205.75   5.606%   $217.2843   $217.28   $217.30   $217.30  
  Purchase #4 $24.87   6.585%   $26.5077   $26.51   $26.50   $26.50  
  Purchase #5 $27.73   7.450%   $29.7959   $29.80   $29.80   $29.80  
  Purchase #6 $114.38   8.665%   $124.291   $124.29   $124.30   $124.30  
  Purchase #7 $179.50   4.117%   $186.89   $186.89   $186.90   $186.90  
  7 purchase totals = $658.14       $700.8217   $700.82   $700.85   $700.80