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	$248.25	12.258%	$278.6805	$278.68	$278.70	$278.70
Purchase #2	$171.71	8.159%	$185.7198	$185.72	$185.70	$185.70
Purchase #3	$18.46	12.278%	$20.7265	$20.73	$20.75	$20.70
Purchase #4	$17.31	4.335%	$18.0604	$18.06	$18.05	$18.10
Purchase #5	$162.42	6.290%	$172.6362	$172.64	$172.65	$172.60
Purchase #6	$243.29	9.856%	$267.2687	$267.27	$267.25	$267.30
Purchase #7	$92.67	12.589%	$104.3362	$104.34	$104.35	$104.30
7 purchase totals =	$954.11		$1,047.4283	$1,047.44	$1,047.45	$1,047.40