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	$52.33	8.648%	$56.8555	$56.86	$56.85	$56.90
Purchase #2	$166.74	7.870%	$179.8624	$179.86	$179.85	$179.90
Purchase #3	$225.28	7.178%	$241.4506	$241.45	$241.45	$241.50
Purchase #4	$239.29	10.318%	$263.9799	$263.98	$264.00	$264.00
Purchase #5	$98.79	9.245%	$107.9231	$107.92	$107.90	$107.90
Purchase #6	$53.53	4.295%	$55.8291	$55.83	$55.85	$55.80
Purchase #7	$36.93	5.109%	$38.8168	$38.82	$38.80	$38.80
7 purchase totals =	$872.89		$944.7174	$944.72	$944.70	$944.80