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 $82.88   3.212%   $85.5421   $85.54   $85.55   $85.50  
  Purchase #2 $14.36   13.179%   $16.2525   $16.25   $16.25   $16.30  
  Purchase #3 $119.36   11.233%   $132.7677   $132.77   $132.75   $132.80  
  Purchase #4 $108.78   5.861%   $115.1556   $115.16   $115.15   $115.20  
  Purchase #5 $247.33   11.146%   $274.8974   $274.90   $274.90   $274.90  
  Purchase #6 $89.87   7.814%   $96.8924   $96.89   $96.90   $96.90  
  Purchase #7 $12.89   5.354%   $13.5801   $13.58   $13.60   $13.60  
  7 purchase totals = $675.47       $735.0878   $735.09   $735.10   $735.20