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	$20.95	9.308%	$22.9	$22.90	$22.90	$22.90
Purchase #2	$62.55	9.196%	$68.3021	$68.30	$68.30	$68.30
Purchase #3	$224.48	8.401%	$243.3386	$243.34	$243.35	$243.30
Purchase #4	$78.46	8.522%	$85.1464	$85.15	$85.15	$85.10
Purchase #5	$146.39	4.832%	$153.4636	$153.46	$153.45	$153.50
Purchase #6	$22.32	9.691%	$24.483	$24.48	$24.50	$24.50
Purchase #7	$20.35	4.466%	$21.2588	$21.26	$21.25	$21.30
7 purchase totals =	$575.50		$618.8925	$618.89	$618.90	$618.90