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	$248.73	11.677%	$277.7742	$277.77	$277.75	$277.80
Purchase #2	$176.47	5.753%	$186.6223	$186.62	$186.60	$186.60
Purchase #3	$65.67	10.534%	$72.5877	$72.59	$72.60	$72.60
Purchase #4	$43.45	12.467%	$48.8669	$48.87	$48.85	$48.90
Purchase #5	$157.38	5.729%	$166.3963	$166.40	$166.40	$166.40
Purchase #6	$186.94	4.543%	$195.4327	$195.43	$195.45	$195.40
Purchase #7	$49.85	11.475%	$55.5703	$55.57	$55.55	$55.60
7 purchase totals =	$928.49		$1,003.2504	$1,003.25	$1,003.20	$1,003.30