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	$19.41	9.729%	$21.2984	$21.30	$21.30	$21.30
Purchase #2	$124.62	11.764%	$139.2803	$139.28	$139.30	$139.30
Purchase #3	$29.72	10.741%	$32.9122	$32.91	$32.90	$32.90
Purchase #4	$186.56	12.500%	$209.88	$209.88	$209.90	$209.90
Purchase #5	$74.92	4.227%	$78.0869	$78.09	$78.10	$78.10
Purchase #6	$180.96	5.388%	$190.7101	$190.71	$190.70	$190.70
Purchase #7	$47.49	4.810%	$49.7743	$49.77	$49.75	$49.80
7 purchase totals =	$663.68		$721.9422	$721.94	$721.95	$722.00