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	$5.52	10.462%	$6.0975	$6.10	$6.10	$6.10
Purchase #2	$171.62	11.265%	$190.953	$190.95	$190.95	$191.00
Purchase #3	$21.51	12.256%	$24.1463	$24.15	$24.15	$24.10
Purchase #4	$78.37	5.606%	$82.7634	$82.76	$82.75	$82.80
Purchase #5	$24.76	4.326%	$25.8311	$25.83	$25.85	$25.80
Purchase #6	$152.93	5.185%	$160.8594	$160.86	$160.85	$160.90
Purchase #7	$148.31	8.663%	$161.1581	$161.16	$161.15	$161.20
7 purchase totals =	$603.02		$651.8088	$651.81	$651.80	$651.90