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	$137.31	13.162%	$155.3827	$155.38	$155.40	$155.40
Purchase #2	$90.91	9.416%	$99.4701	$99.47	$99.45	$99.50
Purchase #3	$128.69	5.119%	$135.2776	$135.28	$135.30	$135.30
Purchase #4	$49.73	3.370%	$51.4059	$51.41	$51.40	$51.40
Purchase #5	$41.92	7.795%	$45.1877	$45.19	$45.20	$45.20
Purchase #6	$192.67	12.832%	$217.3934	$217.39	$217.40	$217.40
Purchase #7	$156.33	10.378%	$172.5539	$172.55	$172.55	$172.60
7 purchase totals =	$797.56		$876.6713	$876.67	$876.70	$876.80