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	$48.68	11.223%	$54.1434	$54.14	$54.15	$54.10
Purchase #2	$112.28	13.636%	$127.5905	$127.59	$127.60	$127.60
Purchase #3	$17.67	6.616%	$18.839	$18.84	$18.85	$18.80
Purchase #4	$65.72	9.507%	$71.968	$71.97	$71.95	$72.00
Purchase #5	$92.76	3.225%	$95.7515	$95.75	$95.75	$95.80
Purchase #6	$40.46	7.399%	$43.4536	$43.45	$43.45	$43.50
Purchase #7	$111.94	7.290%	$120.1004	$120.10	$120.10	$120.10
7 purchase totals =	$489.51		$531.8464	$531.84	$531.85	$531.90