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	$233.83	9.726%	$256.5723	$256.57	$256.55	$256.60
Purchase #2	$35.85	6.140%	$38.0512	$38.05	$38.05	$38.10
Purchase #3	$109.77	9.741%	$120.4627	$120.46	$120.45	$120.50
Purchase #4	$233.58	9.252%	$255.1908	$255.19	$255.20	$255.20
Purchase #5	$148.54	4.280%	$154.8975	$154.90	$154.90	$154.90
Purchase #6	$195.28	13.866%	$222.3575	$222.36	$222.35	$222.40
Purchase #7	$175.71	4.324%	$183.3077	$183.31	$183.30	$183.30
7 purchase totals =	$1,132.56		$1,230.8397	$1,230.84	$1,230.80	$1,231.00