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	$33.90	11.185%	$37.6917	$37.69	$37.70	$37.70
Purchase #2	$167.79	7.175%	$179.8289	$179.83	$179.85	$179.80
Purchase #3	$20.95	8.201%	$22.6681	$22.67	$22.65	$22.70
Purchase #4	$26.89	6.822%	$28.7244	$28.72	$28.70	$28.70
Purchase #5	$58.61	4.153%	$61.0441	$61.04	$61.05	$61.00
Purchase #6	$108.42	3.180%	$111.8678	$111.87	$111.85	$111.90
Purchase #7	$212.83	7.491%	$228.7731	$228.77	$228.75	$228.80
7 purchase totals =	$629.39		$670.5981	$670.59	$670.55	$670.60