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	$24.29	13.609%	$27.5956	$27.60	$27.60	$27.60
Purchase #2	$218.63	13.721%	$248.6282	$248.63	$248.65	$248.60
Purchase #3	$55.60	3.469%	$57.5288	$57.53	$57.55	$57.50
Purchase #4	$140.93	7.707%	$151.7915	$151.79	$151.80	$151.80
Purchase #5	$129.84	11.626%	$144.9352	$144.94	$144.95	$144.90
Purchase #6	$213.56	11.513%	$238.1472	$238.15	$238.15	$238.10
Purchase #7	$94.93	5.562%	$100.21	$100.21	$100.20	$100.20
7 purchase totals =	$877.78		$968.8365	$968.85	$968.90	$968.70