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	$87.49	3.469%	$90.525	$90.53	$90.55	$90.50
Purchase #2	$114.28	12.725%	$128.8221	$128.82	$128.80	$128.80
Purchase #3	$97.78	9.103%	$106.6809	$106.68	$106.70	$106.70
Purchase #4	$214.88	13.259%	$243.3709	$243.37	$243.35	$243.40
Purchase #5	$139.60	11.474%	$155.6177	$155.62	$155.60	$155.60
Purchase #6	$126.41	5.485%	$133.3436	$133.34	$133.35	$133.30
Purchase #7	$147.74	9.756%	$162.1535	$162.15	$162.15	$162.20
7 purchase totals =	$928.18		$1,020.5137	$1,020.51	$1,020.50	$1,020.50