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 $62.99   4.812%   $66.0211   $66.02   $66.00   $66.00  
  Purchase #2 $188.64   13.446%   $214.0045   $214.00   $214.00   $214.00  
  Purchase #3 $174.48   11.108%   $193.8612   $193.86   $193.85   $193.90  
  Purchase #4 $242.92   3.555%   $251.5558   $251.56   $251.55   $251.60  
  Purchase #5 $188.27   13.757%   $214.1703   $214.17   $214.15   $214.20  
  Purchase #6 $179.71   7.381%   $192.9744   $192.97   $192.95   $193.00  
  Purchase #7 $102.92   6.811%   $109.9299   $109.93   $109.95   $109.90  
  7 purchase totals = $1,139.93       $1,242.5172   $1,242.51   $1,242.45   $1,242.60