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	$46.92	3.127%	$48.3872	$48.39	$48.40	$48.40
Purchase #2	$20.65	3.611%	$21.3957	$21.40	$21.40	$21.40
Purchase #3	$130.64	11.687%	$145.9079	$145.91	$145.90	$145.90
Purchase #4	$151.67	13.730%	$172.4943	$172.49	$172.50	$172.50
Purchase #5	$156.47	6.247%	$166.2447	$166.24	$166.25	$166.20
Purchase #6	$203.78	12.425%	$229.0997	$229.10	$229.10	$229.10
Purchase #7	$89.49	8.798%	$97.3633	$97.36	$97.35	$97.40
7 purchase totals =	$799.62		$880.8928	$880.89	$880.90	$880.90