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	$115.92	12.647%	$130.5804	$130.58	$130.60	$130.60
Purchase #2	$49.58	10.109%	$54.592	$54.59	$54.60	$54.60
Purchase #3	$229.97	3.761%	$238.6192	$238.62	$238.60	$238.60
Purchase #4	$226.90	12.520%	$255.3079	$255.31	$255.30	$255.30
Purchase #5	$249.79	8.604%	$271.2819	$271.28	$271.30	$271.30
Purchase #6	$230.83	8.756%	$251.0415	$251.04	$251.05	$251.00
Purchase #7	$86.35	6.324%	$91.8108	$91.81	$91.80	$91.80
7 purchase totals =	$1,189.34		$1,293.2337	$1,293.23	$1,293.25	$1,293.20