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	$209.29	5.654%	$221.1233	$221.12	$221.10	$221.10
Purchase #2	$240.44	9.834%	$264.0849	$264.08	$264.10	$264.10
Purchase #3	$75.82	7.614%	$81.5929	$81.59	$81.60	$81.60
Purchase #4	$214.57	11.259%	$238.7284	$238.73	$238.75	$238.70
Purchase #5	$138.94	10.203%	$153.116	$153.12	$153.10	$153.10
Purchase #6	$130.87	10.411%	$144.4949	$144.49	$144.50	$144.50
Purchase #7	$7.45	13.615%	$8.4643	$8.46	$8.45	$8.50
7 purchase totals =	$1,017.38		$1,111.6047	$1,111.59	$1,111.60	$1,111.60