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	$93.90	10.326%	$103.5961	$103.60	$103.60	$103.60
Purchase #2	$231.41	4.682%	$242.2446	$242.24	$242.25	$242.20
Purchase #3	$217.37	11.431%	$242.2176	$242.22	$242.20	$242.20
Purchase #4	$51.85	4.454%	$54.1594	$54.16	$54.15	$54.20
Purchase #5	$221.56	9.492%	$242.5905	$242.59	$242.60	$242.60
Purchase #6	$110.43	11.502%	$123.1317	$123.13	$123.15	$123.10
Purchase #7	$161.61	13.509%	$183.4419	$183.44	$183.45	$183.40
7 purchase totals =	$1,088.13		$1,191.3818	$1,191.38	$1,191.40	$1,191.30