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	$25.73	11.840%	$28.7764	$28.78	$28.80	$28.80
Purchase #2	$214.61	13.834%	$244.2991	$244.30	$244.30	$244.30
Purchase #3	$238.69	12.173%	$267.7457	$267.75	$267.75	$267.70
Purchase #4	$204.89	13.790%	$233.1443	$233.14	$233.15	$233.10
Purchase #5	$89.39	13.208%	$101.1966	$101.20	$101.20	$101.20
Purchase #6	$237.32	4.816%	$248.7493	$248.75	$248.75	$248.70
Purchase #7	$105.71	5.145%	$111.1488	$111.15	$111.15	$111.10
7 purchase totals =	$1,116.34		$1,235.0602	$1,235.07	$1,235.10	$1,234.90