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 $185.63   11.482%   $206.944   $206.94   $206.95   $206.90  
  Purchase #2 $137.49   3.454%   $142.2389   $142.24   $142.25   $142.20  
  Purchase #3 $15.87   12.606%   $17.8706   $17.87   $17.85   $17.90  
  Purchase #4 $157.28   5.386%   $165.7511   $165.75   $165.75   $165.80  
  Purchase #5 $68.47   10.285%   $75.5121   $75.51   $75.50   $75.50  
  Purchase #6 $67.90   11.648%   $75.809   $75.81   $75.80   $75.80  
  Purchase #7 $97.70   4.298%   $101.8991   $101.90   $101.90   $101.90  
  7 purchase totals = $730.34       $786.0248   $786.02   $786.00   $786.00