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	$242.42	5.510%	$255.7773	$255.78	$255.80	$255.80
Purchase #2	$205.77	8.450%	$223.1576	$223.16	$223.15	$223.20
Purchase #3	$221.54	10.572%	$244.9612	$244.96	$244.95	$245.00
Purchase #4	$223.69	10.293%	$246.7144	$246.71	$246.70	$246.70
Purchase #5	$129.82	12.834%	$146.4811	$146.48	$146.50	$146.50
Purchase #6	$154.32	9.294%	$168.6625	$168.66	$168.65	$168.70
Purchase #7	$128.62	10.570%	$142.2151	$142.22	$142.20	$142.20
7 purchase totals =	$1,306.18		$1,427.9692	$1,427.97	$1,427.95	$1,428.10