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 $242.97   9.789%   $266.7543   $266.75   $266.75   $266.80  
  Purchase #2 $247.76   8.341%   $268.4257   $268.43   $268.45   $268.40  
  Purchase #3 $198.34   7.696%   $213.6042   $213.60   $213.60   $213.60  
  Purchase #4 $110.98   5.280%   $116.8397   $116.84   $116.85   $116.80  
  Purchase #5 $205.25   4.470%   $214.4247   $214.42   $214.40   $214.40  
  Purchase #6 $231.91   7.861%   $250.1404   $250.14   $250.15   $250.10  
  Purchase #7 $19.72   3.795%   $20.4684   $20.47   $20.45   $20.50  
  7 purchase totals = $1,256.93       $1,350.6574   $1,350.65   $1,350.65   $1,350.60