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	$51.39	3.793%	$53.3392	$53.34	$53.35	$53.30
Purchase #2	$56.32	10.704%	$62.3485	$62.35	$62.35	$62.30
Purchase #3	$33.86	12.768%	$38.1832	$38.18	$38.20	$38.20
Purchase #4	$121.67	7.569%	$130.8792	$130.88	$130.90	$130.90
Purchase #5	$130.87	11.575%	$146.0182	$146.02	$146.00	$146.00
Purchase #6	$28.82	12.846%	$32.5222	$32.52	$32.50	$32.50
Purchase #7	$23.55	8.563%	$25.5666	$25.57	$25.55	$25.60
7 purchase totals =	$446.48		$488.8571	$488.86	$488.85	$488.80