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	$18.76	4.671%	$19.6363	$19.64	$19.65	$19.60
Purchase #2	$116.71	10.452%	$128.9085	$128.91	$128.90	$128.90
Purchase #3	$205.35	8.334%	$222.4639	$222.46	$222.45	$222.50
Purchase #4	$62.54	12.330%	$70.2512	$70.25	$70.25	$70.30
Purchase #5	$29.93	11.815%	$33.4662	$33.47	$33.45	$33.50
Purchase #6	$228.54	11.862%	$255.6494	$255.65	$255.65	$255.60
Purchase #7	$72.32	11.669%	$80.759	$80.76	$80.75	$80.80
7 purchase totals =	$734.15		$811.1345	$811.14	$811.10	$811.20