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	$67.42	9.579%	$73.8782	$73.88	$73.90	$73.90
Purchase #2	$85.76	3.855%	$89.066	$89.07	$89.05	$89.10
Purchase #3	$114.35	11.403%	$127.3893	$127.39	$127.40	$127.40
Purchase #4	$158.63	10.787%	$175.7414	$175.74	$175.75	$175.70
Purchase #5	$86.99	4.217%	$90.6584	$90.66	$90.65	$90.70
Purchase #6	$131.57	8.772%	$143.1113	$143.11	$143.10	$143.10
Purchase #7	$9.56	11.365%	$10.6465	$10.65	$10.65	$10.60
7 purchase totals =	$654.28		$710.4911	$710.50	$710.50	$710.50