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	$56.27	6.569%	$59.9664	$59.97	$59.95	$60.00
Purchase #2	$233.61	4.247%	$243.5314	$243.53	$243.55	$243.50
Purchase #3	$92.38	3.761%	$95.8544	$95.85	$95.85	$95.90
Purchase #4	$176.70	7.368%	$189.7193	$189.72	$189.70	$189.70
Purchase #5	$214.32	6.179%	$227.5628	$227.56	$227.55	$227.60
Purchase #6	$207.94	9.346%	$227.3741	$227.37	$227.35	$227.40
Purchase #7	$20.68	10.243%	$22.7983	$22.80	$22.80	$22.80
7 purchase totals =	$1,001.90		$1,066.8067	$1,066.80	$1,066.75	$1,066.90