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 $92.77   9.564%   $101.6425   $101.64   $101.65   $101.60  
  Purchase #2 $86.86   7.472%   $93.3502   $93.35   $93.35   $93.40  
  Purchase #3 $114.79   9.594%   $125.803   $125.80   $125.80   $125.80  
  Purchase #4 $141.81   11.149%   $157.6204   $157.62   $157.60   $157.60  
  Purchase #5 $37.64   13.431%   $42.6954   $42.70   $42.70   $42.70  
  Purchase #6 $164.82   11.796%   $184.2622   $184.26   $184.25   $184.30  
  Purchase #7 $133.29   8.389%   $144.4717   $144.47   $144.45   $144.50  
  7 purchase totals = $771.98       $849.8454   $849.84   $849.80   $849.90