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	$11.56	5.385%	$12.1825	$12.18	$12.20	$12.20
Purchase #2	$81.57	11.776%	$91.1757	$91.18	$91.20	$91.20
Purchase #3	$78.54	6.752%	$83.843	$83.84	$83.85	$83.80
Purchase #4	$39.37	13.294%	$44.6038	$44.60	$44.60	$44.60
Purchase #5	$220.50	9.535%	$241.5247	$241.52	$241.50	$241.50
Purchase #6	$232.97	10.540%	$257.525	$257.53	$257.55	$257.50
Purchase #7	$86.86	4.102%	$90.423	$90.42	$90.40	$90.40
7 purchase totals =	$751.37		$821.2777	$821.27	$821.30	$821.20