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	$82.52	11.674%	$92.1534	$92.15	$92.15	$92.20
Purchase #2	$103.83	4.624%	$108.6311	$108.63	$108.65	$108.60
Purchase #3	$87.61	13.432%	$99.3778	$99.38	$99.40	$99.40
Purchase #4	$135.86	6.548%	$144.7561	$144.76	$144.75	$144.80
Purchase #5	$80.89	9.171%	$88.3084	$88.31	$88.30	$88.30
Purchase #6	$235.70	6.120%	$250.1248	$250.12	$250.10	$250.10
Purchase #7	$49.56	5.444%	$52.258	$52.26	$52.25	$52.30
7 purchase totals =	$775.97		$835.6096	$835.61	$835.60	$835.70