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	$239.51	13.324%	$271.4223	$271.42	$271.40	$271.40
Purchase #2	$218.68	10.742%	$242.1706	$242.17	$242.15	$242.20
Purchase #3	$54.70	11.489%	$60.9845	$60.98	$61.00	$61.00
Purchase #4	$244.86	4.264%	$255.3008	$255.30	$255.30	$255.30
Purchase #5	$76.28	12.507%	$85.8203	$85.82	$85.80	$85.80
Purchase #6	$105.47	11.711%	$117.8216	$117.82	$117.80	$117.80
Purchase #7	$213.45	4.537%	$223.1342	$223.13	$223.15	$223.10
7 purchase totals =	$1,152.95		$1,256.6543	$1,256.64	$1,256.60	$1,256.60