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 $88.82   7.677%   $95.6387   $95.64   $95.65   $95.60  
  Purchase #2 $185.46   9.271%   $202.654   $202.65   $202.65   $202.70  
  Purchase #3 $15.47   6.206%   $16.4301   $16.43   $16.45   $16.40  
  Purchase #4 $96.64   8.129%   $104.4959   $104.50   $104.50   $104.50  
  Purchase #5 $195.60   12.609%   $220.2632   $220.26   $220.25   $220.30  
  Purchase #6 $83.38   10.455%   $92.0974   $92.10   $92.10   $92.10  
  Purchase #7 $129.43   10.248%   $142.694   $142.69   $142.70   $142.70  
  7 purchase totals = $794.80       $874.2733   $874.27   $874.30   $874.30