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	$243.84	7.632%	$262.4499	$262.45	$262.45	$262.40
Purchase #2	$44.89	11.562%	$50.0802	$50.08	$50.10	$50.10
Purchase #3	$24.57	12.652%	$27.6786	$27.68	$27.70	$27.70
Purchase #4	$145.82	4.255%	$152.0246	$152.02	$152.00	$152.00
Purchase #5	$220.52	13.287%	$249.8205	$249.82	$249.80	$249.80
Purchase #6	$81.67	10.384%	$90.1506	$90.15	$90.15	$90.20
Purchase #7	$147.35	13.765%	$167.6327	$167.63	$167.65	$167.60
7 purchase totals =	$908.66		$999.8371	$999.83	$999.85	$999.80