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	$62.68	6.473%	$66.7373	$66.74	$66.75	$66.70
Purchase #2	$13.38	6.288%	$14.2213	$14.22	$14.20	$14.20
Purchase #3	$223.71	10.475%	$247.1436	$247.14	$247.15	$247.10
Purchase #4	$99.80	5.194%	$104.9836	$104.98	$105.00	$105.00
Purchase #5	$10.89	6.600%	$11.6087	$11.61	$11.60	$11.60
Purchase #6	$246.69	13.746%	$280.6	$280.60	$280.60	$280.60
Purchase #7	$143.41	10.835%	$158.9485	$158.95	$158.95	$158.90
7 purchase totals =	$800.56		$884.2430	$884.24	$884.25	$884.10