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	$154.50	7.372%	$165.8897	$165.89	$165.90	$165.90
Purchase #2	$135.63	3.124%	$139.8671	$139.87	$139.85	$139.90
Purchase #3	$149.52	6.354%	$159.0205	$159.02	$159.00	$159.00
Purchase #4	$70.58	10.741%	$78.161	$78.16	$78.15	$78.20
Purchase #5	$193.30	13.857%	$220.0856	$220.09	$220.10	$220.10
Purchase #6	$79.75	4.193%	$83.0939	$83.09	$83.10	$83.10
Purchase #7	$132.78	13.230%	$150.3468	$150.35	$150.35	$150.30
7 purchase totals =	$916.06		$996.4646	$996.47	$996.45	$996.50