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	$74.92	10.496%	$82.7836	$82.78	$82.80	$82.80
Purchase #2	$144.25	4.659%	$150.9706	$150.97	$150.95	$151.00
Purchase #3	$178.84	3.849%	$185.7236	$185.72	$185.70	$185.70
Purchase #4	$192.65	11.168%	$214.1652	$214.17	$214.15	$214.20
Purchase #5	$85.52	3.735%	$88.7142	$88.71	$88.70	$88.70
Purchase #6	$83.31	5.184%	$87.6288	$87.63	$87.65	$87.60
Purchase #7	$27.30	7.480%	$29.342	$29.34	$29.35	$29.30
7 purchase totals =	$786.79		$839.3280	$839.32	$839.30	$839.30