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	$87.49	13.794%	$99.5584	$99.56	$99.55	$99.60
Purchase #2	$193.66	8.586%	$210.2876	$210.29	$210.30	$210.30
Purchase #3	$227.89	11.537%	$254.1817	$254.18	$254.20	$254.20
Purchase #4	$230.54	6.548%	$245.6358	$245.64	$245.65	$245.60
Purchase #5	$75.57	13.140%	$85.4999	$85.50	$85.50	$85.50
Purchase #6	$247.96	9.841%	$272.3617	$272.36	$272.35	$272.40
Purchase #7	$122.75	8.225%	$132.8462	$132.85	$132.85	$132.80
7 purchase totals =	$1,185.86		$1,300.3713	$1,300.38	$1,300.40	$1,300.40