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	$185.50	11.657%	$207.1237	$207.12	$207.10	$207.10
Purchase #2	$250.64	11.243%	$278.8195	$278.82	$278.80	$278.80
Purchase #3	$73.48	13.659%	$83.5166	$83.52	$83.50	$83.50
Purchase #4	$18.82	7.377%	$20.2084	$20.21	$20.20	$20.20
Purchase #5	$180.59	5.724%	$190.927	$190.93	$190.95	$190.90
Purchase #6	$49.71	13.499%	$56.4204	$56.42	$56.40	$56.40
Purchase #7	$142.93	12.345%	$160.5747	$160.57	$160.55	$160.60
7 purchase totals =	$901.67		$997.5903	$997.59	$997.50	$997.50