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	$9.98	4.698%	$10.4489	$10.45	$10.45	$10.40
Purchase #2	$30.75	5.814%	$32.5378	$32.54	$32.55	$32.50
Purchase #3	$18.29	3.225%	$18.8799	$18.88	$18.90	$18.90
Purchase #4	$156.74	12.108%	$175.7181	$175.72	$175.70	$175.70
Purchase #5	$203.66	7.639%	$219.2176	$219.22	$219.20	$219.20
Purchase #6	$209.51	5.499%	$221.031	$221.03	$221.05	$221.00
Purchase #7	$100.96	13.489%	$114.5785	$114.58	$114.60	$114.60
7 purchase totals =	$729.89		$792.4118	$792.42	$792.45	$792.30