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	$17.53	13.102%	$19.8268	$19.83	$19.85	$19.80
Purchase #2	$235.25	4.145%	$245.0011	$245.00	$245.00	$245.00
Purchase #3	$19.45	11.736%	$21.7327	$21.73	$21.75	$21.70
Purchase #4	$52.61	5.461%	$55.483	$55.48	$55.50	$55.50
Purchase #5	$171.38	4.483%	$179.063	$179.06	$179.05	$179.10
Purchase #6	$41.32	10.688%	$45.7363	$45.74	$45.75	$45.70
Purchase #7	$19.94	9.112%	$21.7569	$21.76	$21.75	$21.80
7 purchase totals =	$557.48		$588.5998	$588.60	$588.65	$588.60