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	$80.83	11.771%	$90.3445	$90.34	$90.35	$90.30
Purchase #2	$20.40	5.846%	$21.5926	$21.59	$21.60	$21.60
Purchase #3	$33.83	8.343%	$36.6524	$36.65	$36.65	$36.70
Purchase #4	$6.37	7.616%	$6.8551	$6.86	$6.85	$6.90
Purchase #5	$198.77	7.788%	$214.2502	$214.25	$214.25	$214.30
Purchase #6	$82.56	10.826%	$91.4979	$91.50	$91.50	$91.50
Purchase #7	$54.61	11.609%	$60.9497	$60.95	$60.95	$60.90
7 purchase totals =	$477.37		$522.1424	$522.14	$522.15	$522.20