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	$82.92	8.744%	$90.1705	$90.17	$90.15	$90.20
Purchase #2	$148.55	4.248%	$154.8604	$154.86	$154.85	$154.90
Purchase #3	$75.59	4.381%	$78.9016	$78.90	$78.90	$78.90
Purchase #4	$201.88	10.672%	$223.4246	$223.42	$223.40	$223.40
Purchase #5	$47.58	9.794%	$52.24	$52.24	$52.25	$52.20
Purchase #6	$75.94	4.846%	$79.6201	$79.62	$79.60	$79.60
Purchase #7	$45.65	13.602%	$51.8593	$51.86	$51.85	$51.90
7 purchase totals =	$678.11		$731.0765	$731.07	$731.00	$731.10