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	$173.40	3.677%	$179.7759	$179.78	$179.80	$179.80
Purchase #2	$141.49	5.200%	$148.8475	$148.85	$148.85	$148.80
Purchase #3	$85.48	4.202%	$89.0719	$89.07	$89.05	$89.10
Purchase #4	$223.64	8.617%	$242.9111	$242.91	$242.90	$242.90
Purchase #5	$110.68	3.235%	$114.2605	$114.26	$114.25	$114.30
Purchase #6	$194.61	4.419%	$203.2098	$203.21	$203.20	$203.20
Purchase #7	$150.34	10.685%	$166.4038	$166.40	$166.40	$166.40
7 purchase totals =	$1,079.64		$1,144.4805	$1,144.48	$1,144.45	$1,144.50