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	$159.96	12.390%	$179.779	$179.78	$179.80	$179.80
Purchase #2	$232.89	13.483%	$264.2906	$264.29	$264.30	$264.30
Purchase #3	$42.90	5.191%	$45.1269	$45.13	$45.15	$45.10
Purchase #4	$9.55	8.746%	$10.3852	$10.39	$10.40	$10.40
Purchase #5	$44.87	11.765%	$50.149	$50.15	$50.15	$50.10
Purchase #6	$127.66	12.268%	$143.3213	$143.32	$143.30	$143.30
Purchase #7	$161.25	7.502%	$173.347	$173.35	$173.35	$173.30
7 purchase totals =	$779.08		$866.3990	$866.41	$866.45	$866.30