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	$98.45	10.223%	$108.5145	$108.51	$108.50	$108.50
Purchase #2	$110.73	3.468%	$114.5701	$114.57	$114.55	$114.60
Purchase #3	$102.61	13.329%	$116.2869	$116.29	$116.30	$116.30
Purchase #4	$27.81	5.437%	$29.322	$29.32	$29.30	$29.30
Purchase #5	$136.78	10.737%	$151.4661	$151.47	$151.45	$151.50
Purchase #6	$192.54	13.405%	$218.35	$218.35	$218.35	$218.40
Purchase #7	$143.30	6.350%	$152.3996	$152.40	$152.40	$152.40
7 purchase totals =	$812.22		$890.9092	$890.91	$890.85	$891.00