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	$9.35	8.138%	$10.1109	$10.11	$10.10	$10.10
Purchase #2	$160.81	3.552%	$166.522	$166.52	$166.50	$166.50
Purchase #3	$246.82	13.475%	$280.079	$280.08	$280.10	$280.10
Purchase #4	$98.98	10.556%	$109.4283	$109.43	$109.45	$109.40
Purchase #5	$136.70	3.618%	$141.6458	$141.65	$141.65	$141.60
Purchase #6	$153.43	7.693%	$165.2334	$165.23	$165.25	$165.20
Purchase #7	$240.76	12.214%	$270.1664	$270.17	$270.15	$270.20
7 purchase totals =	$1,046.85		$1,143.1858	$1,143.19	$1,143.20	$1,143.10