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	$75.95	3.486%	$78.5976	$78.60	$78.60	$78.60
Purchase #2	$60.86	3.137%	$62.7692	$62.77	$62.75	$62.80
Purchase #3	$211.69	13.662%	$240.6111	$240.61	$240.60	$240.60
Purchase #4	$56.26	9.521%	$61.6165	$61.62	$61.60	$61.60
Purchase #5	$33.31	9.598%	$36.5071	$36.51	$36.50	$36.50
Purchase #6	$95.42	13.193%	$108.0088	$108.01	$108.00	$108.00
Purchase #7	$228.56	4.381%	$238.5732	$238.57	$238.55	$238.60
7 purchase totals =	$762.05		$826.6835	$826.69	$826.60	$826.70