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	$140.56	10.636%	$155.51	$155.51	$155.50	$155.50
Purchase #2	$83.59	8.223%	$90.4636	$90.46	$90.45	$90.50
Purchase #3	$244.69	12.641%	$275.6213	$275.62	$275.60	$275.60
Purchase #4	$66.46	4.260%	$69.2912	$69.29	$69.30	$69.30
Purchase #5	$187.99	4.454%	$196.3631	$196.36	$196.35	$196.40
Purchase #6	$57.52	6.532%	$61.2772	$61.28	$61.30	$61.30
Purchase #7	$126.99	9.415%	$138.9461	$138.95	$138.95	$138.90
7 purchase totals =	$907.80		$987.4725	$987.47	$987.45	$987.50