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	$143.87	8.298%	$155.8083	$155.81	$155.80	$155.80
Purchase #2	$56.64	4.591%	$59.2403	$59.24	$59.25	$59.20
Purchase #3	$51.80	9.706%	$56.8277	$56.83	$56.85	$56.80
Purchase #4	$64.73	5.407%	$68.23	$68.23	$68.25	$68.20
Purchase #5	$48.58	12.860%	$54.8274	$54.83	$54.85	$54.80
Purchase #6	$110.81	5.450%	$116.8491	$116.85	$116.85	$116.80
Purchase #7	$100.91	8.196%	$109.1806	$109.18	$109.20	$109.20
7 purchase totals =	$577.34		$620.9634	$620.97	$621.05	$620.80