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	$151.49	11.173%	$168.416	$168.42	$168.40	$168.40
Purchase #2	$245.54	4.350%	$256.221	$256.22	$256.20	$256.20
Purchase #3	$180.72	5.231%	$190.1735	$190.17	$190.15	$190.20
Purchase #4	$132.31	6.165%	$140.4669	$140.47	$140.45	$140.50
Purchase #5	$197.41	12.627%	$222.337	$222.34	$222.35	$222.30
Purchase #6	$241.67	5.190%	$254.2127	$254.21	$254.20	$254.20
Purchase #7	$59.84	9.333%	$65.4249	$65.42	$65.40	$65.40
7 purchase totals =	$1,208.98		$1,297.2520	$1,297.25	$1,297.15	$1,297.20