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	$46.41	10.149%	$51.1202	$51.12	$51.10	$51.10
Purchase #2	$143.41	11.411%	$159.7745	$159.77	$159.75	$159.80
Purchase #3	$77.60	4.803%	$81.3271	$81.33	$81.35	$81.30
Purchase #4	$78.33	13.642%	$89.0158	$89.02	$89.00	$89.00
Purchase #5	$176.61	4.431%	$184.4356	$184.44	$184.45	$184.40
Purchase #6	$84.81	4.212%	$88.3822	$88.38	$88.40	$88.40
Purchase #7	$142.54	11.830%	$159.4025	$159.40	$159.40	$159.40
7 purchase totals =	$749.71		$813.4579	$813.46	$813.45	$813.40