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	$23.85	13.301%	$27.0223	$27.02	$27.00	$27.00
Purchase #2	$80.61	13.308%	$91.3376	$91.34	$91.35	$91.30
Purchase #3	$162.55	6.763%	$173.5433	$173.54	$173.55	$173.50
Purchase #4	$17.76	9.845%	$19.5085	$19.51	$19.50	$19.50
Purchase #5	$144.82	9.553%	$158.6547	$158.65	$158.65	$158.70
Purchase #6	$62.77	7.476%	$67.4627	$67.46	$67.45	$67.50
Purchase #7	$73.75	7.596%	$79.3521	$79.35	$79.35	$79.40
7 purchase totals =	$566.11		$616.8812	$616.87	$616.85	$616.90