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	$51.46	10.537%	$56.8823	$56.88	$56.90	$56.90
Purchase #2	$62.56	10.431%	$69.0856	$69.09	$69.10	$69.10
Purchase #3	$154.87	10.635%	$171.3404	$171.34	$171.35	$171.30
Purchase #4	$209.46	8.828%	$227.9511	$227.95	$227.95	$228.00
Purchase #5	$15.96	11.285%	$17.7611	$17.76	$17.75	$17.80
Purchase #6	$107.55	3.277%	$111.0744	$111.07	$111.05	$111.10
Purchase #7	$63.32	13.281%	$71.7295	$71.73	$71.75	$71.70
7 purchase totals =	$665.18		$725.8244	$725.82	$725.85	$725.90