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	$61.32	9.431%	$67.1031	$67.10	$67.10	$67.10
Purchase #2	$206.60	5.164%	$217.2688	$217.27	$217.25	$217.30
Purchase #3	$131.87	3.514%	$136.5039	$136.50	$136.50	$136.50
Purchase #4	$32.38	5.764%	$34.2464	$34.25	$34.25	$34.20
Purchase #5	$117.58	8.334%	$127.3791	$127.38	$127.40	$127.40
Purchase #6	$127.30	7.299%	$136.5916	$136.59	$136.60	$136.60
Purchase #7	$57.47	7.478%	$61.7676	$61.77	$61.75	$61.80
7 purchase totals =	$734.52		$780.8605	$780.86	$780.85	$780.90