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	$29.64	8.618%	$32.1944	$32.19	$32.20	$32.20
Purchase #2	$89.58	11.102%	$99.5252	$99.53	$99.55	$99.50
Purchase #3	$236.47	11.822%	$264.4255	$264.43	$264.45	$264.40
Purchase #4	$77.94	6.519%	$83.0209	$83.02	$83.00	$83.00
Purchase #5	$137.28	6.605%	$146.3473	$146.35	$146.35	$146.30
Purchase #6	$66.79	8.766%	$72.6448	$72.64	$72.65	$72.60
Purchase #7	$103.99	3.151%	$107.2667	$107.27	$107.25	$107.30
7 purchase totals =	$741.69		$805.4248	$805.43	$805.45	$805.30