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	$136.51	5.694%	$144.2829	$144.28	$144.30	$144.30
Purchase #2	$94.53	5.286%	$99.5269	$99.53	$99.55	$99.50
Purchase #3	$239.95	6.435%	$255.3908	$255.39	$255.40	$255.40
Purchase #4	$31.56	13.845%	$35.9295	$35.93	$35.95	$35.90
Purchase #5	$218.35	9.552%	$239.2068	$239.21	$239.20	$239.20
Purchase #6	$113.57	3.499%	$117.5438	$117.54	$117.55	$117.50
Purchase #7	$76.88	11.623%	$85.8158	$85.82	$85.80	$85.80
7 purchase totals =	$911.35		$977.6965	$977.70	$977.75	$977.60