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	$32.30	5.407%	$34.0465	$34.05	$34.05	$34.00
Purchase #2	$250.68	11.723%	$280.0672	$280.07	$280.05	$280.10
Purchase #3	$104.58	11.758%	$116.8765	$116.88	$116.90	$116.90
Purchase #4	$20.59	7.453%	$22.1246	$22.12	$22.10	$22.10
Purchase #5	$74.69	10.175%	$82.2897	$82.29	$82.30	$82.30
Purchase #6	$35.56	10.556%	$39.3137	$39.31	$39.30	$39.30
Purchase #7	$203.89	6.580%	$217.306	$217.31	$217.30	$217.30
7 purchase totals =	$722.29		$792.0242	$792.03	$792.00	$792.00