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 $216.36   13.752%   $246.1138   $246.11   $246.10   $246.10  
  Purchase #2 $168.41   8.475%   $182.6827   $182.68   $182.70   $182.70  
  Purchase #3 $117.41   5.552%   $123.9286   $123.93   $123.95   $123.90  
  Purchase #4 $95.27   13.309%   $107.9495   $107.95   $107.95   $107.90  
  Purchase #5 $162.36   8.125%   $175.5518   $175.55   $175.55   $175.60  
  Purchase #6 $163.83   13.450%   $185.8651   $185.87   $185.85   $185.90  
  Purchase #7 $50.53   4.529%   $52.8185   $52.82   $52.80   $52.80  
  7 purchase totals = $974.17       $1,074.9100   $1,074.91   $1,074.90   $1,074.90