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	$6.81	10.777%	$7.5439	$7.54	$7.55	$7.50
Purchase #2	$77.39	5.766%	$81.8523	$81.85	$81.85	$81.90
Purchase #3	$96.68	3.422%	$99.9884	$99.99	$100.00	$100.00
Purchase #4	$18.95	6.238%	$20.1321	$20.13	$20.15	$20.10
Purchase #5	$108.80	11.121%	$120.8996	$120.90	$120.90	$120.90
Purchase #6	$117.41	9.568%	$128.6438	$128.64	$128.65	$128.60
Purchase #7	$111.31	10.844%	$123.3805	$123.38	$123.40	$123.40
7 purchase totals =	$537.35		$582.4406	$582.43	$582.50	$582.40