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	$83.56	3.540%	$86.518	$86.52	$86.50	$86.50
Purchase #2	$8.44	9.782%	$9.2656	$9.27	$9.25	$9.30
Purchase #3	$55.40	11.225%	$61.6187	$61.62	$61.60	$61.60
Purchase #4	$92.34	12.274%	$103.6738	$103.67	$103.65	$103.70
Purchase #5	$86.28	7.701%	$92.9244	$92.92	$92.90	$92.90
Purchase #6	$111.41	5.486%	$117.522	$117.52	$117.50	$117.50
Purchase #7	$156.51	10.349%	$172.7072	$172.71	$172.70	$172.70
7 purchase totals =	$593.94		$644.2297	$644.23	$644.10	$644.20