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	$15.60	5.870%	$16.5157	$16.52	$16.50	$16.50
Purchase #2	$202.46	6.423%	$215.464	$215.46	$215.45	$215.50
Purchase #3	$192.38	10.834%	$213.2224	$213.22	$213.20	$213.20
Purchase #4	$92.71	8.421%	$100.5171	$100.52	$100.50	$100.50
Purchase #5	$53.70	11.113%	$59.6677	$59.67	$59.65	$59.70
Purchase #6	$241.32	13.347%	$273.529	$273.53	$273.55	$273.50
Purchase #7	$16.52	3.742%	$17.1382	$17.14	$17.15	$17.10
7 purchase totals =	$814.69		$896.0541	$896.06	$896.00	$896.00