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	$15.40	3.613%	$15.9564	$15.96	$15.95	$16.00
Purchase #2	$178.50	7.242%	$191.427	$191.43	$191.45	$191.40
Purchase #3	$83.56	6.567%	$89.0474	$89.05	$89.05	$89.00
Purchase #4	$79.51	13.793%	$90.4768	$90.48	$90.50	$90.50
Purchase #5	$205.79	9.684%	$225.7187	$225.72	$225.70	$225.70
Purchase #6	$11.53	9.509%	$12.6264	$12.63	$12.65	$12.60
Purchase #7	$202.48	12.344%	$227.4741	$227.47	$227.45	$227.50
7 purchase totals =	$776.77		$852.7268	$852.74	$852.75	$852.70