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	$98.77	3.680%	$102.4047	$102.40	$102.40	$102.40
Purchase #2	$38.90	4.228%	$40.5447	$40.54	$40.55	$40.50
Purchase #3	$33.60	7.237%	$36.0316	$36.03	$36.05	$36.00
Purchase #4	$10.92	10.142%	$12.0275	$12.03	$12.05	$12.00
Purchase #5	$147.81	9.850%	$162.3693	$162.37	$162.35	$162.40
Purchase #6	$99.59	12.284%	$111.8236	$111.82	$111.80	$111.80
Purchase #7	$227.31	13.391%	$257.7491	$257.75	$257.75	$257.70
7 purchase totals =	$656.90		$722.9505	$722.94	$722.95	$722.80