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	$21.61	5.269%	$22.7486	$22.75	$22.75	$22.70
Purchase #2	$118.59	7.482%	$127.4629	$127.46	$127.45	$127.50
Purchase #3	$172.42	11.285%	$191.8776	$191.88	$191.90	$191.90
Purchase #4	$152.72	4.811%	$160.0674	$160.07	$160.05	$160.10
Purchase #5	$136.87	13.437%	$155.2612	$155.26	$155.25	$155.30
Purchase #6	$194.33	7.340%	$208.5938	$208.59	$208.60	$208.60
Purchase #7	$100.96	8.186%	$109.2246	$109.22	$109.20	$109.20
7 purchase totals =	$897.50		$975.2361	$975.23	$975.20	$975.30