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	$91.97	11.654%	$102.6882	$102.69	$102.70	$102.70
Purchase #2	$84.59	5.261%	$89.0403	$89.04	$89.05	$89.00
Purchase #3	$124.28	7.410%	$133.4891	$133.49	$133.50	$133.50
Purchase #4	$32.42	12.542%	$36.4861	$36.49	$36.50	$36.50
Purchase #5	$55.86	3.163%	$57.6269	$57.63	$57.65	$57.60
Purchase #6	$52.77	10.569%	$58.3473	$58.35	$58.35	$58.30
Purchase #7	$89.44	12.245%	$100.3919	$100.39	$100.40	$100.40
7 purchase totals =	$531.33		$578.0698	$578.08	$578.15	$578.00