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	$11.63	7.222%	$12.4699	$12.47	$12.45	$12.50
Purchase #2	$66.99	4.632%	$70.093	$70.09	$70.10	$70.10
Purchase #3	$199.36	6.688%	$212.6932	$212.69	$212.70	$212.70
Purchase #4	$104.72	6.397%	$111.4189	$111.42	$111.40	$111.40
Purchase #5	$247.63	4.642%	$259.125	$259.13	$259.15	$259.10
Purchase #6	$233.48	9.118%	$254.7687	$254.77	$254.75	$254.80
Purchase #7	$201.61	4.776%	$211.2389	$211.24	$211.25	$211.20
7 purchase totals =	$1,065.42		$1,131.8076	$1,131.81	$1,131.80	$1,131.80