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	$156.31	6.728%	$166.8265	$166.83	$166.85	$166.80
Purchase #2	$119.29	9.766%	$130.9399	$130.94	$130.95	$130.90
Purchase #3	$221.70	6.371%	$235.8245	$235.82	$235.80	$235.80
Purchase #4	$106.36	7.211%	$114.0296	$114.03	$114.05	$114.00
Purchase #5	$106.83	4.786%	$111.9429	$111.94	$111.95	$111.90
Purchase #6	$10.27	9.188%	$11.2136	$11.21	$11.20	$11.20
Purchase #7	$152.91	10.851%	$169.5023	$169.50	$169.50	$169.50
7 purchase totals =	$873.67		$940.2793	$940.27	$940.30	$940.10