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	$168.85	13.410%	$191.4928	$191.49	$191.50	$191.50
Purchase #2	$143.50	13.440%	$162.7864	$162.79	$162.80	$162.80
Purchase #3	$112.51	12.114%	$126.1395	$126.14	$126.15	$126.10
Purchase #4	$100.78	10.411%	$111.2722	$111.27	$111.25	$111.30
Purchase #5	$54.66	3.489%	$56.5671	$56.57	$56.55	$56.60
Purchase #6	$112.92	4.136%	$117.5904	$117.59	$117.60	$117.60
Purchase #7	$114.46	6.732%	$122.1654	$122.17	$122.15	$122.20
7 purchase totals =	$807.68		$888.0138	$888.02	$888.00	$888.10