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	$220.66	13.802%	$251.1155	$251.12	$251.10	$251.10
Purchase #2	$167.59	10.547%	$185.2657	$185.27	$185.25	$185.30
Purchase #3	$52.67	6.696%	$56.1968	$56.20	$56.20	$56.20
Purchase #4	$40.40	4.651%	$42.279	$42.28	$42.30	$42.30
Purchase #5	$84.60	5.440%	$89.2022	$89.20	$89.20	$89.20
Purchase #6	$179.39	7.266%	$192.4245	$192.42	$192.40	$192.40
Purchase #7	$77.30	12.572%	$87.0182	$87.02	$87.00	$87.00
7 purchase totals =	$822.61		$903.5019	$903.51	$903.45	$903.50