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	$209.72	6.807%	$223.9956	$224.00	$224.00	$224.00
Purchase #2	$112.33	4.456%	$117.3354	$117.34	$117.35	$117.30
Purchase #3	$250.87	11.848%	$280.5931	$280.59	$280.60	$280.60
Purchase #4	$191.66	6.393%	$203.9128	$203.91	$203.90	$203.90
Purchase #5	$137.80	4.471%	$143.961	$143.96	$143.95	$144.00
Purchase #6	$109.55	8.464%	$118.8223	$118.82	$118.80	$118.80
Purchase #7	$10.25	10.422%	$11.3183	$11.32	$11.30	$11.30
7 purchase totals =	$1,022.18		$1,099.9385	$1,099.94	$1,099.90	$1,099.90