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	$98.87	6.542%	$105.3381	$105.34	$105.35	$105.30
Purchase #2	$123.89	12.392%	$139.2424	$139.24	$139.25	$139.20
Purchase #3	$158.67	8.505%	$172.1649	$172.16	$172.15	$172.20
Purchase #4	$180.63	3.559%	$187.0586	$187.06	$187.05	$187.10
Purchase #5	$45.61	8.277%	$49.3851	$49.39	$49.40	$49.40
Purchase #6	$128.86	12.746%	$145.2845	$145.28	$145.30	$145.30
Purchase #7	$179.34	3.410%	$185.4555	$185.46	$185.45	$185.50
7 purchase totals =	$915.87		$983.9291	$983.93	$983.95	$984.00