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	$107.65	6.612%	$114.7678	$114.77	$114.75	$114.80
Purchase #2	$85.33	12.360%	$95.8768	$95.88	$95.90	$95.90
Purchase #3	$29.45	10.845%	$32.6439	$32.64	$32.65	$32.60
Purchase #4	$69.63	11.345%	$77.5295	$77.53	$77.55	$77.50
Purchase #5	$223.88	11.490%	$249.6038	$249.60	$249.60	$249.60
Purchase #6	$124.63	11.770%	$139.299	$139.30	$139.30	$139.30
Purchase #7	$146.73	9.467%	$160.6209	$160.62	$160.60	$160.60
7 purchase totals =	$787.30		$870.3417	$870.34	$870.35	$870.30