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	$25.52	11.278%	$28.3981	$28.40	$28.40	$28.40
Purchase #2	$100.88	8.702%	$109.6586	$109.66	$109.65	$109.70
Purchase #3	$230.76	7.226%	$247.4347	$247.43	$247.45	$247.40
Purchase #4	$30.38	10.173%	$33.4706	$33.47	$33.45	$33.50
Purchase #5	$145.39	11.668%	$162.3541	$162.35	$162.35	$162.40
Purchase #6	$26.72	4.591%	$27.9467	$27.95	$27.95	$27.90
Purchase #7	$142.96	7.111%	$153.1259	$153.13	$153.15	$153.10
7 purchase totals =	$702.61		$762.3887	$762.39	$762.40	$762.40