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	$98.41	11.653%	$109.8777	$109.88	$109.90	$109.90
Purchase #2	$99.85	7.731%	$107.5694	$107.57	$107.55	$107.60
Purchase #3	$71.26	9.684%	$78.1608	$78.16	$78.15	$78.20
Purchase #4	$29.97	6.426%	$31.8959	$31.90	$31.90	$31.90
Purchase #5	$159.97	4.180%	$166.6567	$166.66	$166.65	$166.70
Purchase #6	$36.58	11.297%	$40.7124	$40.71	$40.70	$40.70
Purchase #7	$12.52	5.150%	$13.1648	$13.16	$13.15	$13.20
7 purchase totals =	$508.56		$548.0377	$548.04	$548.00	$548.20