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 $91.49   5.202%   $96.2493   $96.25   $96.25   $96.20  
  Purchase #2 $115.96   6.486%   $123.4812   $123.48   $123.50   $123.50  
  Purchase #3 $104.99   7.362%   $112.7194   $112.72   $112.70   $112.70  
  Purchase #4 $213.71   3.709%   $221.6365   $221.64   $221.65   $221.60  
  Purchase #5 $249.58   7.727%   $268.865   $268.87   $268.85   $268.90  
  Purchase #6 $120.66   8.107%   $130.4419   $130.44   $130.45   $130.40  
  Purchase #7 $13.70   13.542%   $15.5553   $15.56   $15.55   $15.60  
  7 purchase totals = $910.09       $968.9486   $968.96   $968.95   $968.90