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	$140.71	13.602%	$159.8494	$159.85	$159.85	$159.80
Purchase #2	$155.87	12.390%	$175.1823	$175.18	$175.20	$175.20
Purchase #3	$59.96	10.122%	$66.0292	$66.03	$66.05	$66.00
Purchase #4	$72.95	10.635%	$80.7082	$80.71	$80.70	$80.70
Purchase #5	$20.37	7.365%	$21.8703	$21.87	$21.85	$21.90
Purchase #6	$238.37	7.357%	$255.9069	$255.91	$255.90	$255.90
Purchase #7	$111.82	3.174%	$115.3692	$115.37	$115.35	$115.40
7 purchase totals =	$800.05		$874.9155	$874.92	$874.90	$874.90