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	$56.80	4.110%	$59.1345	$59.13	$59.15	$59.10
Purchase #2	$21.27	10.691%	$23.544	$23.54	$23.55	$23.50
Purchase #3	$144.98	12.215%	$162.6893	$162.69	$162.70	$162.70
Purchase #4	$144.75	9.173%	$158.0279	$158.03	$158.05	$158.00
Purchase #5	$13.91	11.768%	$15.5469	$15.55	$15.55	$15.50
Purchase #6	$82.59	8.648%	$89.7324	$89.73	$89.75	$89.70
Purchase #7	$111.91	3.570%	$115.9052	$115.91	$115.90	$115.90
7 purchase totals =	$576.21		$624.5802	$624.58	$624.65	$624.40