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	$50.40	7.862%	$54.3624	$54.36	$54.35	$54.40
Purchase #2	$242.62	5.144%	$255.1004	$255.10	$255.10	$255.10
Purchase #3	$33.82	13.741%	$38.4672	$38.47	$38.45	$38.50
Purchase #4	$9.29	10.473%	$10.2629	$10.26	$10.25	$10.30
Purchase #5	$236.95	9.601%	$259.6996	$259.70	$259.70	$259.70
Purchase #6	$94.26	6.736%	$100.6094	$100.61	$100.60	$100.60
Purchase #7	$170.34	12.368%	$191.4077	$191.41	$191.40	$191.40
7 purchase totals =	$837.68		$909.9096	$909.91	$909.85	$910.00