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	$37.43	4.536%	$39.1278	$39.13	$39.15	$39.10
Purchase #2	$211.52	13.614%	$240.3163	$240.32	$240.30	$240.30
Purchase #3	$81.67	5.259%	$85.965	$85.97	$85.95	$86.00
Purchase #4	$73.44	5.243%	$77.2905	$77.29	$77.30	$77.30
Purchase #5	$60.92	3.258%	$62.9048	$62.90	$62.90	$62.90
Purchase #6	$114.53	12.189%	$128.4901	$128.49	$128.50	$128.50
Purchase #7	$135.42	11.738%	$151.3156	$151.32	$151.30	$151.30
7 purchase totals =	$714.93		$785.4101	$785.42	$785.40	$785.40