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	$69.33	12.751%	$78.1703	$78.17	$78.15	$78.20
Purchase #2	$227.54	12.408%	$255.7732	$255.77	$255.75	$255.80
Purchase #3	$26.62	11.557%	$29.6965	$29.70	$29.70	$29.70
Purchase #4	$55.74	11.678%	$62.2493	$62.25	$62.25	$62.20
Purchase #5	$122.47	6.560%	$130.504	$130.50	$130.50	$130.50
Purchase #6	$227.99	4.730%	$238.7739	$238.77	$238.75	$238.80
Purchase #7	$85.88	11.324%	$95.6051	$95.61	$95.60	$95.60
7 purchase totals =	$815.57		$890.7723	$890.77	$890.70	$890.80