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	$230.59	11.715%	$257.6036	$257.60	$257.60	$257.60
Purchase #2	$208.36	7.129%	$223.214	$223.21	$223.20	$223.20
Purchase #3	$159.80	12.268%	$179.4043	$179.40	$179.40	$179.40
Purchase #4	$54.86	12.590%	$61.7669	$61.77	$61.75	$61.80
Purchase #5	$36.55	4.780%	$38.2971	$38.30	$38.30	$38.30
Purchase #6	$72.93	9.390%	$79.7781	$79.78	$79.80	$79.80
Purchase #7	$96.75	4.152%	$100.7671	$100.77	$100.75	$100.80
7 purchase totals =	$859.84		$940.8311	$940.83	$940.80	$940.90