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	$57.82	5.716%	$61.125	$61.13	$61.15	$61.10
Purchase #2	$174.35	4.331%	$181.9011	$181.90	$181.90	$181.90
Purchase #3	$72.36	13.833%	$82.3696	$82.37	$82.35	$82.40
Purchase #4	$139.27	10.148%	$153.4031	$153.40	$153.40	$153.40
Purchase #5	$139.35	13.626%	$158.3378	$158.34	$158.35	$158.30
Purchase #6	$27.94	6.370%	$29.7198	$29.72	$29.70	$29.70
Purchase #7	$9.57	5.253%	$10.0727	$10.07	$10.05	$10.10
7 purchase totals =	$620.66		$676.9291	$676.93	$676.90	$676.90