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	$139.31	5.236%	$146.6043	$146.60	$146.60	$146.60
Purchase #2	$62.48	9.152%	$68.1982	$68.20	$68.20	$68.20
Purchase #3	$83.58	7.609%	$89.9396	$89.94	$89.95	$89.90
Purchase #4	$140.29	8.454%	$152.1501	$152.15	$152.15	$152.20
Purchase #5	$244.42	4.704%	$255.9175	$255.92	$255.90	$255.90
Purchase #6	$149.74	3.844%	$155.496	$155.50	$155.50	$155.50
Purchase #7	$120.87	8.749%	$131.4449	$131.44	$131.45	$131.40
7 purchase totals =	$940.69		$999.7506	$999.75	$999.75	$999.70