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	$62.70	9.228%	$68.486	$68.49	$68.50	$68.50
Purchase #2	$139.89	8.237%	$151.4127	$151.41	$151.40	$151.40
Purchase #3	$94.87	5.699%	$100.2766	$100.28	$100.30	$100.30
Purchase #4	$38.38	9.675%	$42.0933	$42.09	$42.10	$42.10
Purchase #5	$94.37	10.502%	$104.2807	$104.28	$104.30	$104.30
Purchase #6	$194.32	7.307%	$208.519	$208.52	$208.50	$208.50
Purchase #7	$13.38	9.753%	$14.685	$14.69	$14.70	$14.70
7 purchase totals =	$637.91		$689.7533	$689.76	$689.80	$689.80