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	$172.98	3.860%	$179.657	$179.66	$179.65	$179.70
Purchase #2	$137.77	3.529%	$142.6319	$142.63	$142.65	$142.60
Purchase #3	$75.56	5.779%	$79.9266	$79.93	$79.95	$79.90
Purchase #4	$29.48	6.172%	$31.2995	$31.30	$31.30	$31.30
Purchase #5	$79.45	13.753%	$90.3768	$90.38	$90.40	$90.40
Purchase #6	$235.27	8.650%	$255.6209	$255.62	$255.60	$255.60
Purchase #7	$176.86	10.867%	$196.0794	$196.08	$196.10	$196.10
7 purchase totals =	$907.37		$975.5921	$975.60	$975.65	$975.60