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	$23.95	3.559%	$24.8024	$24.80	$24.80	$24.80
Purchase #2	$98.64	11.125%	$109.6137	$109.61	$109.60	$109.60
Purchase #3	$20.58	6.466%	$21.9107	$21.91	$21.90	$21.90
Purchase #4	$81.54	13.343%	$92.4199	$92.42	$92.40	$92.40
Purchase #5	$141.67	6.650%	$151.0911	$151.09	$151.10	$151.10
Purchase #6	$99.67	5.334%	$104.9864	$104.99	$105.00	$105.00
Purchase #7	$81.65	9.148%	$89.1193	$89.12	$89.10	$89.10
7 purchase totals =	$547.70		$593.9435	$593.94	$593.90	$593.90