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	$105.88	3.647%	$109.7414	$109.74	$109.75	$109.70
Purchase #2	$139.43	7.302%	$149.6112	$149.61	$149.60	$149.60
Purchase #3	$158.69	4.392%	$165.6597	$165.66	$165.65	$165.70
Purchase #4	$9.91	8.129%	$10.7156	$10.72	$10.70	$10.70
Purchase #5	$226.54	10.678%	$250.7299	$250.73	$250.75	$250.70
Purchase #6	$191.78	11.648%	$214.1185	$214.12	$214.10	$214.10
Purchase #7	$80.57	11.107%	$89.5189	$89.52	$89.50	$89.50
7 purchase totals =	$912.80		$990.0952	$990.10	$990.05	$990.00