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	$12.38	5.699%	$13.0855	$13.09	$13.10	$13.10
Purchase #2	$23.98	7.426%	$25.7608	$25.76	$25.75	$25.80
Purchase #3	$95.39	4.528%	$99.7093	$99.71	$99.70	$99.70
Purchase #4	$239.79	3.809%	$248.9236	$248.92	$248.90	$248.90
Purchase #5	$173.26	13.250%	$196.217	$196.22	$196.20	$196.20
Purchase #6	$7.38	5.702%	$7.8008	$7.80	$7.80	$7.80
Purchase #7	$91.32	8.738%	$99.2995	$99.30	$99.30	$99.30
7 purchase totals =	$643.50		$690.7965	$690.80	$690.75	$690.80