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	$75.79	3.740%	$78.6245	$78.62	$78.60	$78.60
Purchase #2	$13.26	13.541%	$15.0555	$15.06	$15.05	$15.10
Purchase #3	$14.93	4.488%	$15.6001	$15.60	$15.60	$15.60
Purchase #4	$209.26	5.712%	$221.2129	$221.21	$221.20	$221.20
Purchase #5	$37.80	10.373%	$41.721	$41.72	$41.70	$41.70
Purchase #6	$94.98	11.120%	$105.5418	$105.54	$105.55	$105.50
Purchase #7	$21.44	6.720%	$22.8808	$22.88	$22.90	$22.90
7 purchase totals =	$467.46		$500.6366	$500.63	$500.60	$500.60