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	$30.49	12.757%	$34.3796	$34.38	$34.40	$34.40
Purchase #2	$113.45	12.507%	$127.6392	$127.64	$127.65	$127.60
Purchase #3	$65.30	7.814%	$70.4025	$70.40	$70.40	$70.40
Purchase #4	$250.93	3.319%	$259.2584	$259.26	$259.25	$259.30
Purchase #5	$136.30	11.184%	$151.5438	$151.54	$151.55	$151.50
Purchase #6	$14.60	6.569%	$15.5591	$15.56	$15.55	$15.60
Purchase #7	$140.39	8.147%	$151.8276	$151.83	$151.85	$151.80
7 purchase totals =	$751.46		$810.6102	$810.61	$810.65	$810.60