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	$75.31	3.763%	$78.1439	$78.14	$78.15	$78.10
Purchase #2	$45.47	4.382%	$47.4625	$47.46	$47.45	$47.50
Purchase #3	$29.59	5.312%	$31.1618	$31.16	$31.15	$31.20
Purchase #4	$220.29	3.766%	$228.5861	$228.59	$228.60	$228.60
Purchase #5	$95.64	5.751%	$101.1403	$101.14	$101.15	$101.10
Purchase #6	$25.39	11.457%	$28.2989	$28.30	$28.30	$28.30
Purchase #7	$64.41	7.332%	$69.1325	$69.13	$69.15	$69.10
7 purchase totals =	$556.10		$583.9260	$583.92	$583.95	$583.90