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	$27.42	13.698%	$31.176	$31.18	$31.20	$31.20
Purchase #2	$55.89	10.643%	$61.8384	$61.84	$61.85	$61.80
Purchase #3	$122.67	4.297%	$127.9411	$127.94	$127.95	$127.90
Purchase #4	$110.53	7.168%	$118.4528	$118.45	$118.45	$118.50
Purchase #5	$243.26	10.772%	$269.464	$269.46	$269.45	$269.50
Purchase #6	$137.45	3.849%	$142.7405	$142.74	$142.75	$142.70
Purchase #7	$19.61	6.310%	$20.8474	$20.85	$20.85	$20.80
7 purchase totals =	$716.83		$772.4602	$772.46	$772.50	$772.40