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	$52.85	4.269%	$55.1062	$55.11	$55.10	$55.10
Purchase #2	$64.29	9.840%	$70.6161	$70.62	$70.60	$70.60
Purchase #3	$68.31	5.561%	$72.1087	$72.11	$72.10	$72.10
Purchase #4	$227.74	10.467%	$251.5775	$251.58	$251.60	$251.60
Purchase #5	$84.38	9.868%	$92.7066	$92.71	$92.70	$92.70
Purchase #6	$12.42	5.152%	$13.0599	$13.06	$13.05	$13.10
Purchase #7	$38.73	12.840%	$43.7029	$43.70	$43.70	$43.70
7 purchase totals =	$548.72		$598.8779	$598.89	$598.85	$598.90