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	$115.57	5.159%	$121.5323	$121.53	$121.55	$121.50
Purchase #2	$12.76	6.464%	$13.5848	$13.58	$13.60	$13.60
Purchase #3	$185.49	4.833%	$194.4547	$194.45	$194.45	$194.50
Purchase #4	$166.94	12.701%	$188.143	$188.14	$188.15	$188.10
Purchase #5	$42.67	9.486%	$46.7177	$46.72	$46.70	$46.70
Purchase #6	$112.77	13.412%	$127.8947	$127.89	$127.90	$127.90
Purchase #7	$176.42	5.396%	$185.9396	$185.94	$185.95	$185.90
7 purchase totals =	$812.62		$878.2668	$878.25	$878.30	$878.20