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	$153.40	5.797%	$162.2926	$162.29	$162.30	$162.30
Purchase #2	$228.52	10.563%	$252.6586	$252.66	$252.65	$252.70
Purchase #3	$169.82	9.358%	$185.7118	$185.71	$185.70	$185.70
Purchase #4	$152.67	5.725%	$161.4104	$161.41	$161.40	$161.40
Purchase #5	$64.58	12.354%	$72.5582	$72.56	$72.55	$72.60
Purchase #6	$192.88	4.134%	$200.8537	$200.85	$200.85	$200.90
Purchase #7	$42.95	12.418%	$48.2835	$48.28	$48.30	$48.30
7 purchase totals =	$1,004.82		$1,083.7688	$1,083.76	$1,083.75	$1,083.90