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	$66.46	6.361%	$70.6875	$70.69	$70.70	$70.70
Purchase #2	$48.87	3.577%	$50.6181	$50.62	$50.60	$50.60
Purchase #3	$250.48	3.768%	$259.9181	$259.92	$259.90	$259.90
Purchase #4	$228.52	13.513%	$259.3999	$259.40	$259.40	$259.40
Purchase #5	$211.40	9.353%	$231.1722	$231.17	$231.15	$231.20
Purchase #6	$33.56	12.404%	$37.7228	$37.72	$37.70	$37.70
Purchase #7	$120.35	6.289%	$127.9188	$127.92	$127.90	$127.90
7 purchase totals =	$959.64		$1,037.4374	$1,037.44	$1,037.35	$1,037.40