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	$240.82	6.133%	$255.5895	$255.59	$255.60	$255.60
Purchase #2	$211.27	10.732%	$233.9435	$233.94	$233.95	$233.90
Purchase #3	$110.51	4.695%	$115.6984	$115.70	$115.70	$115.70
Purchase #4	$48.87	11.517%	$54.4984	$54.50	$54.50	$54.50
Purchase #5	$160.31	11.454%	$178.6719	$178.67	$178.65	$178.70
Purchase #6	$77.49	13.107%	$87.6466	$87.65	$87.65	$87.60
Purchase #7	$237.28	9.367%	$259.506	$259.51	$259.50	$259.50
7 purchase totals =	$1,086.55		$1,185.5543	$1,185.56	$1,185.55	$1,185.50