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	$45.45	10.149%	$50.0627	$50.06	$50.05	$50.10
Purchase #2	$101.75	12.842%	$114.8167	$114.82	$114.80	$114.80
Purchase #3	$136.44	10.480%	$150.7389	$150.74	$150.75	$150.70
Purchase #4	$126.73	7.706%	$136.4958	$136.50	$136.50	$136.50
Purchase #5	$160.43	10.665%	$177.5399	$177.54	$177.55	$177.50
Purchase #6	$91.66	9.426%	$100.2999	$100.30	$100.30	$100.30
Purchase #7	$50.57	11.113%	$56.1898	$56.19	$56.20	$56.20
7 purchase totals =	$713.03		$786.1437	$786.15	$786.15	$786.10