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	$37.71	3.788%	$39.1385	$39.14	$39.15	$39.10
Purchase #2	$79.43	13.104%	$89.8385	$89.84	$89.85	$89.80
Purchase #3	$249.51	8.676%	$271.1575	$271.16	$271.15	$271.20
Purchase #4	$64.53	3.584%	$66.8428	$66.84	$66.85	$66.80
Purchase #5	$56.72	13.443%	$64.3449	$64.34	$64.35	$64.30
Purchase #6	$204.92	12.296%	$230.117	$230.12	$230.10	$230.10
Purchase #7	$205.49	8.456%	$222.8662	$222.87	$222.85	$222.90
7 purchase totals =	$898.31		$984.3054	$984.31	$984.30	$984.20