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 $193.78   3.174%   $199.9306   $199.93   $199.95   $199.90  
  Purchase #2 $213.45   9.430%   $233.5783   $233.58   $233.60   $233.60  
  Purchase #3 $212.28   8.366%   $230.0393   $230.04   $230.05   $230.00  
  Purchase #4 $15.38   5.483%   $16.2233   $16.22   $16.20   $16.20  
  Purchase #5 $84.59   5.446%   $89.1968   $89.20   $89.20   $89.20  
  Purchase #6 $64.37   10.733%   $71.2788   $71.28   $71.30   $71.30  
  Purchase #7 $90.84   9.478%   $99.4498   $99.45   $99.45   $99.40  
  7 purchase totals = $874.69       $939.6969   $939.70   $939.75   $939.60