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	$111.40	6.446%	$118.5808	$118.58	$118.60	$118.60
Purchase #2	$242.75	3.786%	$251.9405	$251.94	$251.95	$251.90
Purchase #3	$189.49	12.365%	$212.9204	$212.92	$212.90	$212.90
Purchase #4	$76.65	7.711%	$82.5605	$82.56	$82.55	$82.60
Purchase #5	$32.95	3.380%	$34.0637	$34.06	$34.05	$34.10
Purchase #6	$205.37	5.474%	$216.612	$216.61	$216.60	$216.60
Purchase #7	$151.93	8.695%	$165.1403	$165.14	$165.15	$165.10
7 purchase totals =	$1,010.54		$1,081.8182	$1,081.81	$1,081.80	$1,081.80