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 $92.80   5.695%   $98.085   $98.09   $98.10   $98.10  
  Purchase #2 $104.96   12.562%   $118.1451   $118.15   $118.15   $118.10  
  Purchase #3 $239.31   5.845%   $253.2977   $253.30   $253.30   $253.30  
  Purchase #4 $90.47   4.733%   $94.7519   $94.75   $94.75   $94.80  
  Purchase #5 $5.73   3.690%   $5.9414   $5.94   $5.95   $5.90  
  Purchase #6 $60.26   8.677%   $65.4888   $65.49   $65.50   $65.50  
  Purchase #7 $93.40   10.804%   $103.4909   $103.49   $103.50   $103.50  
  7 purchase totals = $686.93       $739.2008   $739.21   $739.25   $739.20