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	$35.81	4.690%	$37.4895	$37.49	$37.50	$37.50
Purchase #2	$27.69	11.293%	$30.817	$30.82	$30.80	$30.80
Purchase #3	$188.39	10.705%	$208.5571	$208.56	$208.55	$208.60
Purchase #4	$240.34	5.758%	$254.1788	$254.18	$254.20	$254.20
Purchase #5	$82.56	9.232%	$90.1819	$90.18	$90.20	$90.20
Purchase #6	$19.98	5.252%	$21.0293	$21.03	$21.05	$21.00
Purchase #7	$51.65	5.790%	$54.6405	$54.64	$54.65	$54.60
7 purchase totals =	$646.42		$696.8941	$696.90	$696.95	$696.90