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	$73.79	6.314%	$78.4491	$78.45	$78.45	$78.40
Purchase #2	$53.38	9.449%	$58.4239	$58.42	$58.40	$58.40
Purchase #3	$47.89	8.830%	$52.1187	$52.12	$52.10	$52.10
Purchase #4	$230.44	11.405%	$256.7217	$256.72	$256.70	$256.70
Purchase #5	$38.59	11.660%	$43.0896	$43.09	$43.10	$43.10
Purchase #6	$248.57	12.751%	$280.2652	$280.27	$280.25	$280.30
Purchase #7	$156.52	3.291%	$161.6711	$161.67	$161.65	$161.70
7 purchase totals =	$849.18		$930.7393	$930.74	$930.65	$930.70