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	$160.98	11.698%	$179.8114	$179.81	$179.80	$179.80
Purchase #2	$233.71	3.769%	$242.5185	$242.52	$242.50	$242.50
Purchase #3	$217.68	9.485%	$238.3269	$238.33	$238.35	$238.30
Purchase #4	$165.30	10.340%	$182.392	$182.39	$182.40	$182.40
Purchase #5	$34.86	9.532%	$38.1829	$38.18	$38.20	$38.20
Purchase #6	$81.92	10.804%	$90.7706	$90.77	$90.75	$90.80
Purchase #7	$66.74	10.629%	$73.8338	$73.83	$73.85	$73.80
7 purchase totals =	$961.19		$1,045.8361	$1,045.83	$1,045.85	$1,045.80