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	$75.84	3.205%	$78.2707	$78.27	$78.25	$78.30
Purchase #2	$130.73	6.854%	$139.6902	$139.69	$139.70	$139.70
Purchase #3	$119.64	10.677%	$132.414	$132.41	$132.40	$132.40
Purchase #4	$51.36	9.808%	$56.3974	$56.40	$56.40	$56.40
Purchase #5	$35.97	12.319%	$40.4011	$40.40	$40.40	$40.40
Purchase #6	$112.79	7.391%	$121.1263	$121.13	$121.15	$121.10
Purchase #7	$29.29	12.478%	$32.9448	$32.94	$32.95	$32.90
7 purchase totals =	$555.62		$601.2445	$601.24	$601.25	$601.20