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	$158.56	3.619%	$164.2983	$164.30	$164.30	$164.30
Purchase #2	$78.40	9.414%	$85.7806	$85.78	$85.80	$85.80
Purchase #3	$122.27	13.462%	$138.73	$138.73	$138.75	$138.70
Purchase #4	$17.82	10.640%	$19.716	$19.72	$19.70	$19.70
Purchase #5	$6.62	13.512%	$7.5145	$7.51	$7.50	$7.50
Purchase #6	$114.25	13.802%	$130.0188	$130.02	$130.00	$130.00
Purchase #7	$6.67	9.727%	$7.3188	$7.32	$7.30	$7.30
7 purchase totals =	$504.59		$553.3770	$553.38	$553.35	$553.30