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	$126.26	8.105%	$136.4934	$136.49	$136.50	$136.50
Purchase #2	$40.72	12.586%	$45.845	$45.85	$45.85	$45.80
Purchase #3	$126.80	3.197%	$130.8538	$130.85	$130.85	$130.90
Purchase #4	$20.59	4.462%	$21.5087	$21.51	$21.50	$21.50
Purchase #5	$69.36	11.457%	$77.3066	$77.31	$77.30	$77.30
Purchase #6	$200.99	5.243%	$211.5279	$211.53	$211.55	$211.50
Purchase #7	$19.44	8.304%	$21.0543	$21.05	$21.05	$21.10
7 purchase totals =	$604.16		$644.5897	$644.59	$644.60	$644.60