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	$40.43	5.485%	$42.6476	$42.65	$42.65	$42.60
Purchase #2	$132.83	5.838%	$140.5846	$140.58	$140.60	$140.60
Purchase #3	$153.35	10.528%	$169.4947	$169.49	$169.50	$169.50
Purchase #4	$17.50	9.714%	$19.2	$19.20	$19.20	$19.20
Purchase #5	$180.35	13.535%	$204.7604	$204.76	$204.75	$204.80
Purchase #6	$199.43	11.784%	$222.9308	$222.93	$222.95	$222.90
Purchase #7	$110.56	4.281%	$115.2931	$115.29	$115.30	$115.30
7 purchase totals =	$834.45		$914.9112	$914.90	$914.95	$914.90