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	$49.76	3.274%	$51.3891	$51.39	$51.40	$51.40
Purchase #2	$237.63	10.732%	$263.1325	$263.13	$263.15	$263.10
Purchase #3	$111.92	10.858%	$124.0723	$124.07	$124.05	$124.10
Purchase #4	$103.36	13.328%	$117.1358	$117.14	$117.15	$117.10
Purchase #5	$118.33	7.722%	$127.4674	$127.47	$127.45	$127.50
Purchase #6	$124.35	13.719%	$141.4096	$141.41	$141.40	$141.40
Purchase #7	$37.38	6.115%	$39.6658	$39.67	$39.65	$39.70
7 purchase totals =	$782.73		$864.2725	$864.28	$864.25	$864.30