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	$79.80	8.388%	$86.4936	$86.49	$86.50	$86.50
Purchase #2	$50.52	9.365%	$55.2512	$55.25	$55.25	$55.30
Purchase #3	$49.98	13.141%	$56.5479	$56.55	$56.55	$56.50
Purchase #4	$196.27	8.318%	$212.5957	$212.60	$212.60	$212.60
Purchase #5	$186.52	10.209%	$205.5618	$205.56	$205.55	$205.60
Purchase #6	$241.92	13.108%	$273.6309	$273.63	$273.65	$273.60
Purchase #7	$85.29	3.234%	$88.0483	$88.05	$88.05	$88.00
7 purchase totals =	$890.30		$978.1294	$978.13	$978.15	$978.10