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	$89.95	10.123%	$99.0556	$99.06	$99.05	$99.10
Purchase #2	$123.72	12.620%	$139.3335	$139.33	$139.35	$139.30
Purchase #3	$133.62	9.623%	$146.4783	$146.48	$146.50	$146.50
Purchase #4	$38.31	13.839%	$43.6117	$43.61	$43.60	$43.60
Purchase #5	$240.95	5.862%	$255.0745	$255.07	$255.05	$255.10
Purchase #6	$236.99	6.161%	$251.591	$251.59	$251.60	$251.60
Purchase #7	$193.73	10.531%	$214.1317	$214.13	$214.15	$214.10
7 purchase totals =	$1,057.27		$1,149.2763	$1,149.27	$1,149.30	$1,149.30