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	$158.46	7.581%	$170.4729	$170.47	$170.45	$170.50
Purchase #2	$166.35	4.333%	$173.5579	$173.56	$173.55	$173.60
Purchase #3	$131.34	10.459%	$145.0769	$145.08	$145.10	$145.10
Purchase #4	$51.98	11.428%	$57.9203	$57.92	$57.90	$57.90
Purchase #5	$30.98	12.300%	$34.7905	$34.79	$34.80	$34.80
Purchase #6	$13.55	6.537%	$14.4358	$14.44	$14.45	$14.40
Purchase #7	$111.85	13.694%	$127.1667	$127.17	$127.15	$127.20
7 purchase totals =	$664.51		$723.4210	$723.43	$723.40	$723.50