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	$151.72	4.309%	$158.2576	$158.26	$158.25	$158.30
Purchase #2	$83.42	8.553%	$90.5549	$90.55	$90.55	$90.60
Purchase #3	$165.56	13.508%	$187.9238	$187.92	$187.90	$187.90
Purchase #4	$39.66	6.766%	$42.3434	$42.34	$42.35	$42.30
Purchase #5	$14.53	11.107%	$16.1438	$16.14	$16.15	$16.10
Purchase #6	$41.71	12.295%	$46.8382	$46.84	$46.85	$46.80
Purchase #7	$85.62	3.809%	$88.8813	$88.88	$88.90	$88.90
7 purchase totals =	$582.22		$630.9430	$630.93	$630.95	$630.90