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	$171.56	6.726%	$183.0991	$183.10	$183.10	$183.10
Purchase #2	$143.37	8.754%	$155.9206	$155.92	$155.90	$155.90
Purchase #3	$78.57	6.433%	$83.6244	$83.62	$83.60	$83.60
Purchase #4	$89.87	11.178%	$99.9157	$99.92	$99.90	$99.90
Purchase #5	$55.94	12.159%	$62.7417	$62.74	$62.75	$62.70
Purchase #6	$95.47	4.509%	$99.7747	$99.77	$99.75	$99.80
Purchase #7	$173.94	3.597%	$180.1966	$180.20	$180.20	$180.20
7 purchase totals =	$808.72		$865.2728	$865.27	$865.20	$865.20