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	$20.58	5.503%	$21.7125	$21.71	$21.70	$21.70
Purchase #2	$57.57	9.328%	$62.9401	$62.94	$62.95	$62.90
Purchase #3	$30.45	5.295%	$32.0623	$32.06	$32.05	$32.10
Purchase #4	$78.50	6.799%	$83.8372	$83.84	$83.85	$83.80
Purchase #5	$15.67	6.145%	$16.6329	$16.63	$16.65	$16.60
Purchase #6	$117.74	10.480%	$130.0792	$130.08	$130.10	$130.10
Purchase #7	$85.29	5.674%	$90.1294	$90.13	$90.15	$90.10
7 purchase totals =	$405.80		$437.3936	$437.39	$437.45	$437.30