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 $56.97   10.114%   $62.7319   $62.73   $62.75   $62.70  
  Purchase #2 $169.99   13.759%   $193.3789   $193.38   $193.40   $193.40  
  Purchase #3 $82.35   12.182%   $92.3819   $92.38   $92.40   $92.40  
  Purchase #4 $79.66   12.659%   $89.7442   $89.74   $89.75   $89.70  
  Purchase #5 $214.91   7.228%   $230.4437   $230.44   $230.45   $230.40  
  Purchase #6 $26.81   6.343%   $28.5106   $28.51   $28.50   $28.50  
  Purchase #7 $72.90   12.609%   $82.092   $82.09   $82.10   $82.10  
  7 purchase totals = $703.59       $779.2832   $779.27   $779.35   $779.20