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	$170.57	13.209%	$193.1006	$193.10	$193.10	$193.10
Purchase #2	$142.35	6.258%	$151.2583	$151.26	$151.25	$151.30
Purchase #3	$82.74	11.108%	$91.9308	$91.93	$91.95	$91.90
Purchase #4	$116.56	11.722%	$130.2232	$130.22	$130.20	$130.20
Purchase #5	$148.78	6.416%	$158.3257	$158.33	$158.35	$158.30
Purchase #6	$30.90	9.572%	$33.8577	$33.86	$33.85	$33.90
Purchase #7	$105.99	6.527%	$112.908	$112.91	$112.90	$112.90
7 purchase totals =	$797.89		$871.6043	$871.61	$871.60	$871.60