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	$38.60	6.846%	$41.2426	$41.24	$41.25	$41.20
Purchase #2	$196.51	7.165%	$210.5899	$210.59	$210.60	$210.60
Purchase #3	$246.41	13.865%	$280.5747	$280.57	$280.55	$280.60
Purchase #4	$33.48	10.834%	$37.1072	$37.11	$37.10	$37.10
Purchase #5	$11.38	11.621%	$12.7025	$12.70	$12.70	$12.70
Purchase #6	$48.52	11.466%	$54.0833	$54.08	$54.10	$54.10
Purchase #7	$83.40	9.538%	$91.3547	$91.35	$91.35	$91.40
7 purchase totals =	$658.30		$727.6549	$727.64	$727.65	$727.70