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	$7.56	13.621%	$8.5897	$8.59	$8.60	$8.60
Purchase #2	$142.95	8.602%	$155.2466	$155.25	$155.25	$155.20
Purchase #3	$81.64	13.250%	$92.4573	$92.46	$92.45	$92.50
Purchase #4	$90.34	8.638%	$98.1436	$98.14	$98.15	$98.10
Purchase #5	$173.47	12.548%	$195.237	$195.24	$195.25	$195.20
Purchase #6	$234.84	8.731%	$255.3439	$255.34	$255.35	$255.30
Purchase #7	$223.35	12.321%	$250.869	$250.87	$250.85	$250.90
7 purchase totals =	$954.15		$1,055.8871	$1,055.89	$1,055.90	$1,055.80