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	$239.79	4.725%	$251.1201	$251.12	$251.10	$251.10
Purchase #2	$52.49	12.734%	$59.1741	$59.17	$59.15	$59.20
Purchase #3	$111.34	5.405%	$117.3579	$117.36	$117.35	$117.40
Purchase #4	$66.50	7.297%	$71.3525	$71.35	$71.35	$71.40
Purchase #5	$76.96	7.564%	$82.7813	$82.78	$82.80	$82.80
Purchase #6	$209.49	9.679%	$229.7665	$229.77	$229.75	$229.80
Purchase #7	$117.66	7.780%	$126.8139	$126.81	$126.80	$126.80
7 purchase totals =	$874.23		$938.3663	$938.36	$938.30	$938.50