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	$30.44	3.254%	$31.4305	$31.43	$31.45	$31.40
Purchase #2	$10.98	11.330%	$12.224	$12.22	$12.20	$12.20
Purchase #3	$30.64	6.867%	$32.744	$32.74	$32.75	$32.70
Purchase #4	$90.74	5.312%	$95.5601	$95.56	$95.55	$95.60
Purchase #5	$247.60	4.805%	$259.4972	$259.50	$259.50	$259.50
Purchase #6	$205.42	8.800%	$223.497	$223.50	$223.50	$223.50
Purchase #7	$113.65	4.446%	$118.7029	$118.70	$118.70	$118.70
7 purchase totals =	$729.47		$773.6557	$773.65	$773.65	$773.60