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	$150.86	9.784%	$165.6201	$165.62	$165.60	$165.60
Purchase #2	$42.75	9.722%	$46.9062	$46.91	$46.90	$46.90
Purchase #3	$116.48	8.645%	$126.5497	$126.55	$126.55	$126.50
Purchase #4	$72.86	6.190%	$77.37	$77.37	$77.35	$77.40
Purchase #5	$176.31	5.760%	$186.4655	$186.47	$186.45	$186.50
Purchase #6	$141.80	7.366%	$152.245	$152.25	$152.25	$152.20
Purchase #7	$83.79	5.291%	$88.2233	$88.22	$88.20	$88.20
7 purchase totals =	$784.85		$843.3798	$843.39	$843.30	$843.30