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	$6.92	6.850%	$7.394	$7.39	$7.40	$7.40
Purchase #2	$184.42	7.576%	$198.3917	$198.39	$198.40	$198.40
Purchase #3	$130.47	10.578%	$144.2711	$144.27	$144.25	$144.30
Purchase #4	$215.87	11.429%	$240.5418	$240.54	$240.55	$240.50
Purchase #5	$218.33	10.786%	$241.8791	$241.88	$241.90	$241.90
Purchase #6	$177.31	10.323%	$195.6137	$195.61	$195.60	$195.60
Purchase #7	$136.64	6.667%	$145.7498	$145.75	$145.75	$145.70
7 purchase totals =	$1,069.96		$1,173.8412	$1,173.83	$1,173.85	$1,173.80