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	$45.97	13.365%	$52.1139	$52.11	$52.10	$52.10
Purchase #2	$146.28	9.134%	$159.6412	$159.64	$159.65	$159.60
Purchase #3	$113.65	5.422%	$119.8121	$119.81	$119.80	$119.80
Purchase #4	$173.39	10.117%	$190.9319	$190.93	$190.95	$190.90
Purchase #5	$81.73	4.133%	$85.1079	$85.11	$85.10	$85.10
Purchase #6	$52.99	8.712%	$57.6065	$57.61	$57.60	$57.60
Purchase #7	$111.39	11.694%	$124.4159	$124.42	$124.40	$124.40
7 purchase totals =	$725.40		$789.6294	$789.63	$789.60	$789.50