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	$90.48	4.219%	$94.2974	$94.30	$94.30	$94.30
Purchase #2	$125.27	4.689%	$131.1439	$131.14	$131.15	$131.10
Purchase #3	$89.60	9.547%	$98.1541	$98.15	$98.15	$98.20
Purchase #4	$81.35	9.720%	$89.2572	$89.26	$89.25	$89.30
Purchase #5	$115.42	12.448%	$129.7875	$129.79	$129.80	$129.80
Purchase #6	$11.37	12.856%	$12.8317	$12.83	$12.85	$12.80
Purchase #7	$222.40	11.119%	$247.1287	$247.13	$247.15	$247.10
7 purchase totals =	$735.89		$802.6005	$802.60	$802.65	$802.60