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	$83.88	6.701%	$89.5008	$89.50	$89.50	$89.50
Purchase #2	$26.85	5.271%	$28.2653	$28.27	$28.25	$28.30
Purchase #3	$242.57	5.280%	$255.3777	$255.38	$255.40	$255.40
Purchase #4	$58.66	10.715%	$64.9454	$64.95	$64.95	$64.90
Purchase #5	$104.98	11.197%	$116.7346	$116.73	$116.75	$116.70
Purchase #6	$27.48	5.606%	$29.0205	$29.02	$29.00	$29.00
Purchase #7	$44.95	3.463%	$46.5066	$46.51	$46.50	$46.50
7 purchase totals =	$589.37		$630.3509	$630.36	$630.35	$630.30