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	$29.46	11.371%	$32.8099	$32.81	$32.80	$32.80
Purchase #2	$31.75	6.648%	$33.8607	$33.86	$33.85	$33.90
Purchase #3	$99.61	7.362%	$106.9433	$106.94	$106.95	$106.90
Purchase #4	$109.75	11.426%	$122.29	$122.29	$122.30	$122.30
Purchase #5	$107.49	3.356%	$111.0974	$111.10	$111.10	$111.10
Purchase #6	$179.73	4.545%	$187.8987	$187.90	$187.90	$187.90
Purchase #7	$27.62	7.620%	$29.7246	$29.72	$29.70	$29.70
7 purchase totals =	$585.41		$624.6246	$624.62	$624.60	$624.60