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	$148.50	7.169%	$159.146	$159.15	$159.15	$159.10
Purchase #2	$117.91	5.654%	$124.5766	$124.58	$124.60	$124.60
Purchase #3	$223.76	3.394%	$231.3544	$231.35	$231.35	$231.40
Purchase #4	$174.78	4.274%	$182.2501	$182.25	$182.25	$182.30
Purchase #5	$148.85	10.587%	$164.6087	$164.61	$164.60	$164.60
Purchase #6	$36.76	11.174%	$40.8676	$40.87	$40.85	$40.90
Purchase #7	$9.33	7.717%	$10.05	$10.05	$10.05	$10.10
7 purchase totals =	$859.89		$912.8534	$912.86	$912.85	$913.00