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 $98.69   7.743%   $106.3316   $106.33   $106.35   $106.30  
  Purchase #2 $176.79   8.476%   $191.7747   $191.77   $191.75   $191.80  
  Purchase #3 $174.98   9.708%   $191.9671   $191.97   $191.95   $192.00  
  Purchase #4 $47.46   8.307%   $51.4025   $51.40   $51.40   $51.40  
  Purchase #5 $33.37   7.667%   $35.9285   $35.93   $35.95   $35.90  
  Purchase #6 $192.27   7.169%   $206.0538   $206.05   $206.05   $206.10  
  Purchase #7 $10.38   10.342%   $11.4535   $11.45   $11.45   $11.50  
  7 purchase totals = $733.94       $794.9117   $794.90   $794.90   $795.00