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	$88.44	12.121%	$99.1598	$99.16	$99.15	$99.20
Purchase #2	$168.60	12.661%	$189.9464	$189.95	$189.95	$189.90
Purchase #3	$64.54	4.630%	$67.5282	$67.53	$67.55	$67.50
Purchase #4	$144.59	5.592%	$152.6755	$152.68	$152.70	$152.70
Purchase #5	$105.42	10.283%	$116.2603	$116.26	$116.25	$116.30
Purchase #6	$121.93	8.781%	$132.6367	$132.64	$132.65	$132.60
Purchase #7	$82.88	9.675%	$90.8986	$90.90	$90.90	$90.90
7 purchase totals =	$776.40		$849.1055	$849.12	$849.15	$849.10