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	$67.58	4.255%	$70.4555	$70.46	$70.45	$70.50
Purchase #2	$92.61	5.300%	$97.5183	$97.52	$97.50	$97.50
Purchase #3	$76.54	8.203%	$82.8186	$82.82	$82.80	$82.80
Purchase #4	$18.69	11.689%	$20.8747	$20.87	$20.85	$20.90
Purchase #5	$55.80	4.653%	$58.3964	$58.40	$58.40	$58.40
Purchase #6	$71.69	13.703%	$81.5137	$81.51	$81.50	$81.50
Purchase #7	$74.89	6.206%	$79.5377	$79.54	$79.55	$79.50
7 purchase totals =	$457.80		$491.1149	$491.12	$491.05	$491.10