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	$33.63	3.824%	$34.916	$34.92	$34.90	$34.90
Purchase #2	$122.32	6.612%	$130.4078	$130.41	$130.40	$130.40
Purchase #3	$9.75	4.623%	$10.2007	$10.20	$10.20	$10.20
Purchase #4	$78.67	13.446%	$89.248	$89.25	$89.25	$89.20
Purchase #5	$239.57	10.240%	$264.102	$264.10	$264.10	$264.10
Purchase #6	$99.25	6.262%	$105.465	$105.47	$105.45	$105.50
Purchase #7	$50.43	11.473%	$56.2158	$56.22	$56.20	$56.20
7 purchase totals =	$633.62		$690.5553	$690.57	$690.50	$690.50