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	$15.55	13.300%	$17.6182	$17.62	$17.60	$17.60
Purchase #2	$210.42	11.151%	$233.8839	$233.88	$233.90	$233.90
Purchase #3	$149.85	4.178%	$156.1107	$156.11	$156.10	$156.10
Purchase #4	$198.60	12.621%	$223.6653	$223.67	$223.65	$223.70
Purchase #5	$151.50	10.723%	$167.7453	$167.75	$167.75	$167.70
Purchase #6	$90.30	4.650%	$94.499	$94.50	$94.50	$94.50
Purchase #7	$220.64	6.467%	$234.9088	$234.91	$234.90	$234.90
7 purchase totals =	$1,036.86		$1,128.4312	$1,128.44	$1,128.40	$1,128.40