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	$93.79	5.674%	$99.1116	$99.11	$99.10	$99.10
Purchase #2	$120.91	11.322%	$134.5994	$134.60	$134.60	$134.60
Purchase #3	$225.61	5.772%	$238.6322	$238.63	$238.65	$238.60
Purchase #4	$106.28	6.111%	$112.7748	$112.77	$112.75	$112.80
Purchase #5	$111.75	5.759%	$118.1857	$118.19	$118.20	$118.20
Purchase #6	$32.77	11.686%	$36.5995	$36.60	$36.60	$36.60
Purchase #7	$115.60	4.337%	$120.6136	$120.61	$120.60	$120.60
7 purchase totals =	$806.71		$860.5168	$860.51	$860.50	$860.50