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	$18.54	12.435%	$20.8454	$20.85	$20.85	$20.80
Purchase #2	$181.28	11.206%	$201.5942	$201.59	$201.60	$201.60
Purchase #3	$119.97	10.822%	$132.9532	$132.95	$132.95	$133.00
Purchase #4	$230.54	9.242%	$251.8465	$251.85	$251.85	$251.80
Purchase #5	$123.26	4.521%	$128.8326	$128.83	$128.85	$128.80
Purchase #6	$180.27	8.756%	$196.0544	$196.05	$196.05	$196.10
Purchase #7	$136.87	11.496%	$152.6046	$152.60	$152.60	$152.60
7 purchase totals =	$990.73		$1,084.7309	$1,084.72	$1,084.75	$1,084.70