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 $236.76   13.449%   $268.6019   $268.60   $268.60   $268.60  
  Purchase #2 $117.77   7.654%   $126.7841   $126.78   $126.80   $126.80  
  Purchase #3 $83.95   13.442%   $95.2346   $95.23   $95.25   $95.20  
  Purchase #4 $181.37   4.349%   $189.2578   $189.26   $189.25   $189.30  
  Purchase #5 $199.60   7.684%   $214.9373   $214.94   $214.95   $214.90  
  Purchase #6 $182.25   5.671%   $192.5854   $192.59   $192.60   $192.60  
  Purchase #7 $71.49   7.149%   $76.6008   $76.60   $76.60   $76.60  
  7 purchase totals = $1,073.19       $1,164.0019   $1,164.00   $1,164.05   $1,164.00