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	$127.88	13.615%	$145.2909	$145.29	$145.30	$145.30
Purchase #2	$38.69	10.414%	$42.7192	$42.72	$42.70	$42.70
Purchase #3	$92.91	12.180%	$104.2264	$104.23	$104.25	$104.20
Purchase #4	$53.57	4.825%	$56.1548	$56.15	$56.15	$56.20
Purchase #5	$125.62	7.207%	$134.6734	$134.67	$134.65	$134.70
Purchase #6	$105.76	9.174%	$115.4624	$115.46	$115.45	$115.50
Purchase #7	$44.46	4.343%	$46.3909	$46.39	$46.40	$46.40
7 purchase totals =	$588.89		$644.9180	$644.91	$644.90	$645.00