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 $155.64   7.661%   $167.5636   $167.56   $167.55   $167.60  
  Purchase #2 $103.59   3.576%   $107.2944   $107.29   $107.30   $107.30  
  Purchase #3 $34.69   9.638%   $38.0334   $38.03   $38.05   $38.00  
  Purchase #4 $239.95   6.394%   $255.2924   $255.29   $255.30   $255.30  
  Purchase #5 $192.63   11.129%   $214.0678   $214.07   $214.05   $214.10  
  Purchase #6 $157.49   10.361%   $173.8075   $173.81   $173.80   $173.80  
  Purchase #7 $6.77   11.237%   $7.5307   $7.53   $7.55   $7.50  
  7 purchase totals = $890.76       $963.5898   $963.58   $963.60   $963.60