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	$80.41	11.247%	$89.4537	$89.45	$89.45	$89.50
Purchase #2	$37.77	6.773%	$40.3282	$40.33	$40.35	$40.30
Purchase #3	$10.27	13.864%	$11.6938	$11.69	$11.70	$11.70
Purchase #4	$101.80	4.438%	$106.3179	$106.32	$106.30	$106.30
Purchase #5	$159.50	5.859%	$168.8451	$168.85	$168.85	$168.80
Purchase #6	$102.31	3.552%	$105.9441	$105.94	$105.95	$105.90
Purchase #7	$48.55	11.662%	$54.2119	$54.21	$54.20	$54.20
7 purchase totals =	$540.61		$576.7947	$576.79	$576.80	$576.70