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 $244.67   9.816%   $268.6868   $268.69   $268.70   $268.70  
  Purchase #2 $242.49   8.114%   $262.1656   $262.17   $262.15   $262.20  
  Purchase #3 $141.25   7.462%   $151.7901   $151.79   $151.80   $151.80  
  Purchase #4 $17.49   10.146%   $19.2645   $19.26   $19.25   $19.30  
  Purchase #5 $25.44   12.548%   $28.6322   $28.63   $28.65   $28.60  
  Purchase #6 $204.71   6.376%   $217.7623   $217.76   $217.75   $217.80  
  Purchase #7 $119.49   12.762%   $134.7393   $134.74   $134.75   $134.70  
  7 purchase totals = $995.54       $1,083.0408   $1,083.04   $1,083.05   $1,083.10