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	$170.77	10.244%	$188.2637	$188.26	$188.25	$188.30
Purchase #2	$227.42	7.868%	$245.3134	$245.31	$245.30	$245.30
Purchase #3	$112.84	13.843%	$128.4604	$128.46	$128.45	$128.50
Purchase #4	$248.40	9.325%	$271.5633	$271.56	$271.55	$271.60
Purchase #5	$18.95	11.420%	$21.1141	$21.11	$21.10	$21.10
Purchase #6	$123.34	3.768%	$127.9875	$127.99	$128.00	$128.00
Purchase #7	$226.50	6.353%	$240.8895	$240.89	$240.90	$240.90
7 purchase totals =	$1,128.22		$1,223.5919	$1,223.58	$1,223.55	$1,223.70