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	$83.33	7.345%	$89.4506	$89.45	$89.45	$89.50
Purchase #2	$132.70	10.321%	$146.396	$146.40	$146.40	$146.40
Purchase #3	$47.51	10.325%	$52.4154	$52.42	$52.40	$52.40
Purchase #4	$147.54	5.239%	$155.2696	$155.27	$155.25	$155.30
Purchase #5	$52.86	13.817%	$60.1637	$60.16	$60.15	$60.20
Purchase #6	$154.74	7.193%	$165.8704	$165.87	$165.85	$165.90
Purchase #7	$161.63	13.492%	$183.4371	$183.44	$183.45	$183.40
7 purchase totals =	$780.31		$853.0028	$853.01	$852.95	$853.10