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	$90.52	8.119%	$97.8693	$97.87	$97.85	$97.90
Purchase #2	$89.77	10.523%	$99.2165	$99.22	$99.20	$99.20
Purchase #3	$139.69	9.165%	$152.4926	$152.49	$152.50	$152.50
Purchase #4	$193.61	5.419%	$204.1017	$204.10	$204.10	$204.10
Purchase #5	$159.64	12.798%	$180.0707	$180.07	$180.05	$180.10
Purchase #6	$94.55	13.803%	$107.6007	$107.60	$107.60	$107.60
Purchase #7	$124.29	10.468%	$137.3007	$137.30	$137.30	$137.30
7 purchase totals =	$892.07		$978.6522	$978.65	$978.60	$978.70