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	$179.83	5.261%	$189.2909	$189.29	$189.30	$189.30
Purchase #2	$56.67	5.215%	$59.6253	$59.63	$59.65	$59.60
Purchase #3	$78.40	7.346%	$84.1593	$84.16	$84.15	$84.20
Purchase #4	$227.73	11.703%	$254.3812	$254.38	$254.40	$254.40
Purchase #5	$21.31	5.357%	$22.4516	$22.45	$22.45	$22.50
Purchase #6	$119.43	9.274%	$130.5059	$130.51	$130.50	$130.50
Purchase #7	$59.45	4.769%	$62.2852	$62.29	$62.30	$62.30
7 purchase totals =	$742.82		$802.6994	$802.71	$802.75	$802.80