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	$174.77	8.609%	$189.8159	$189.82	$189.80	$189.80
Purchase #2	$51.85	3.209%	$53.5139	$53.51	$53.50	$53.50
Purchase #3	$137.40	11.229%	$152.8286	$152.83	$152.85	$152.80
Purchase #4	$28.95	12.549%	$32.5829	$32.58	$32.60	$32.60
Purchase #5	$92.69	3.741%	$96.1575	$96.16	$96.15	$96.20
Purchase #6	$68.40	8.358%	$74.1169	$74.12	$74.10	$74.10
Purchase #7	$248.65	6.803%	$265.5657	$265.57	$265.55	$265.60
7 purchase totals =	$802.71		$864.5814	$864.59	$864.55	$864.60