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	$12.61	4.477%	$13.1745	$13.17	$13.15	$13.20
Purchase #2	$234.94	8.371%	$254.6068	$254.61	$254.60	$254.60
Purchase #3	$33.69	11.190%	$37.4599	$37.46	$37.45	$37.50
Purchase #4	$108.72	13.430%	$123.3211	$123.32	$123.30	$123.30
Purchase #5	$90.72	7.690%	$97.6964	$97.70	$97.70	$97.70
Purchase #6	$111.99	4.401%	$116.9187	$116.92	$116.90	$116.90
Purchase #7	$181.82	7.302%	$195.0965	$195.10	$195.10	$195.10
7 purchase totals =	$774.49		$838.2739	$838.28	$838.20	$838.30