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	$32.79	13.340%	$37.1642	$37.16	$37.15	$37.20
Purchase #2	$197.95	8.407%	$214.5917	$214.59	$214.60	$214.60
Purchase #3	$121.38	10.575%	$134.2159	$134.22	$134.20	$134.20
Purchase #4	$25.47	11.850%	$28.4882	$28.49	$28.50	$28.50
Purchase #5	$63.65	10.496%	$70.3307	$70.33	$70.35	$70.30
Purchase #6	$59.51	9.314%	$65.0528	$65.05	$65.05	$65.10
Purchase #7	$168.71	10.594%	$186.5831	$186.58	$186.60	$186.60
7 purchase totals =	$669.46		$736.4266	$736.42	$736.45	$736.50