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	$90.71	9.150%	$99.01	$99.01	$99.00	$99.00
Purchase #2	$49.67	7.745%	$53.5169	$53.52	$53.50	$53.50
Purchase #3	$127.60	13.368%	$144.6576	$144.66	$144.65	$144.70
Purchase #4	$147.77	5.578%	$156.0126	$156.01	$156.00	$156.00
Purchase #5	$17.34	4.341%	$18.0927	$18.09	$18.10	$18.10
Purchase #6	$123.71	5.120%	$130.044	$130.04	$130.05	$130.00
Purchase #7	$8.52	3.175%	$8.7905	$8.79	$8.80	$8.80
7 purchase totals =	$565.32		$610.1243	$610.12	$610.10	$610.10