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	$146.61	6.815%	$156.6015	$156.60	$156.60	$156.60
Purchase #2	$100.31	8.746%	$109.0831	$109.08	$109.10	$109.10
Purchase #3	$127.99	5.179%	$134.6186	$134.62	$134.60	$134.60
Purchase #4	$44.75	6.663%	$47.7317	$47.73	$47.75	$47.70
Purchase #5	$115.32	13.842%	$131.2826	$131.28	$131.30	$131.30
Purchase #6	$198.55	9.871%	$218.1489	$218.15	$218.15	$218.10
Purchase #7	$12.30	5.151%	$12.9336	$12.93	$12.95	$12.90
7 purchase totals =	$745.83		$810.4000	$810.39	$810.45	$810.30