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	$40.31	4.416%	$42.0901	$42.09	$42.10	$42.10
Purchase #2	$64.32	13.401%	$72.9395	$72.94	$72.95	$72.90
Purchase #3	$84.56	9.704%	$92.7657	$92.77	$92.75	$92.80
Purchase #4	$138.82	11.394%	$154.6372	$154.64	$154.65	$154.60
Purchase #5	$102.90	11.154%	$114.3775	$114.38	$114.40	$114.40
Purchase #6	$217.55	13.467%	$246.8475	$246.85	$246.85	$246.80
Purchase #7	$54.58	3.745%	$56.624	$56.62	$56.60	$56.60
7 purchase totals =	$703.04		$780.2815	$780.29	$780.30	$780.20