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	$10.25	5.249%	$10.788	$10.79	$10.80	$10.80
Purchase #2	$80.56	5.221%	$84.766	$84.77	$84.75	$84.80
Purchase #3	$247.39	11.346%	$275.4589	$275.46	$275.45	$275.50
Purchase #4	$53.38	13.541%	$60.6082	$60.61	$60.60	$60.60
Purchase #5	$33.52	11.622%	$37.4157	$37.42	$37.40	$37.40
Purchase #6	$49.84	9.648%	$54.6486	$54.65	$54.65	$54.60
Purchase #7	$45.56	4.763%	$47.73	$47.73	$47.75	$47.70
7 purchase totals =	$520.50		$571.4154	$571.43	$571.40	$571.40