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 $82.76   12.686%   $93.2589   $93.26   $93.25   $93.30  
  Purchase #2 $167.45   6.785%   $178.8115   $178.81   $178.80   $178.80  
  Purchase #3 $241.97   12.690%   $272.676   $272.68   $272.70   $272.70  
  Purchase #4 $13.38   11.633%   $14.9365   $14.94   $14.95   $14.90  
  Purchase #5 $131.33   9.460%   $143.7538   $143.75   $143.75   $143.80  
  Purchase #6 $27.58   13.626%   $31.3381   $31.34   $31.35   $31.30  
  Purchase #7 $118.47   8.120%   $128.0898   $128.09   $128.10   $128.10  
  7 purchase totals = $782.94       $862.8646   $862.87   $862.90   $862.90