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	$37.81	12.770%	$42.6383	$42.64	$42.65	$42.60
Purchase #2	$114.31	13.303%	$129.5167	$129.52	$129.50	$129.50
Purchase #3	$153.59	5.425%	$161.9223	$161.92	$161.90	$161.90
Purchase #4	$58.57	4.226%	$61.0452	$61.05	$61.05	$61.00
Purchase #5	$241.98	11.868%	$270.6982	$270.70	$270.70	$270.70
Purchase #6	$53.44	10.866%	$59.2468	$59.25	$59.25	$59.20
Purchase #7	$137.71	5.671%	$145.5195	$145.52	$145.50	$145.50
7 purchase totals =	$797.41		$870.5870	$870.60	$870.55	$870.40