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	$25.56	10.417%	$28.2226	$28.22	$28.20	$28.20
Purchase #2	$205.40	9.320%	$224.5433	$224.54	$224.55	$224.50
Purchase #3	$157.32	8.281%	$170.3477	$170.35	$170.35	$170.30
Purchase #4	$98.49	13.157%	$111.4483	$111.45	$111.45	$111.40
Purchase #5	$241.82	5.674%	$255.5409	$255.54	$255.55	$255.50
Purchase #6	$95.73	3.465%	$99.047	$99.05	$99.05	$99.00
Purchase #7	$15.84	13.199%	$17.9307	$17.93	$17.95	$17.90
7 purchase totals =	$840.16		$907.0805	$907.08	$907.10	$906.80