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	$41.81	11.178%	$46.4835	$46.48	$46.50	$46.50
Purchase #2	$249.76	12.721%	$281.532	$281.53	$281.55	$281.50
Purchase #3	$110.85	5.386%	$116.8204	$116.82	$116.80	$116.80
Purchase #4	$143.37	3.547%	$148.4553	$148.46	$148.45	$148.50
Purchase #5	$20.35	4.426%	$21.2507	$21.25	$21.25	$21.30
Purchase #6	$115.87	12.248%	$130.0618	$130.06	$130.05	$130.10
Purchase #7	$167.83	9.728%	$184.1565	$184.16	$184.15	$184.20
7 purchase totals =	$849.84		$928.7602	$928.76	$928.75	$928.90