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	$99.77	11.740%	$111.483	$111.48	$111.50	$111.50
Purchase #2	$142.54	12.599%	$160.4986	$160.50	$160.50	$160.50
Purchase #3	$96.86	6.550%	$103.2043	$103.20	$103.20	$103.20
Purchase #4	$65.86	11.441%	$73.395	$73.40	$73.40	$73.40
Purchase #5	$15.64	10.495%	$17.2814	$17.28	$17.30	$17.30
Purchase #6	$233.30	10.145%	$256.9683	$256.97	$256.95	$257.00
Purchase #7	$164.90	12.141%	$184.9205	$184.92	$184.90	$184.90
7 purchase totals =	$818.87		$907.7511	$907.75	$907.75	$907.80