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	$58.54	10.335%	$64.5901	$64.59	$64.60	$64.60
Purchase #2	$66.81	4.858%	$70.0556	$70.06	$70.05	$70.10
Purchase #3	$133.52	8.489%	$144.8545	$144.85	$144.85	$144.90
Purchase #4	$208.56	12.474%	$234.5758	$234.58	$234.60	$234.60
Purchase #5	$91.32	7.844%	$98.4831	$98.48	$98.50	$98.50
Purchase #6	$42.84	6.845%	$45.7724	$45.77	$45.75	$45.80
Purchase #7	$102.42	11.418%	$114.1143	$114.11	$114.10	$114.10
7 purchase totals =	$704.01		$772.4458	$772.44	$772.45	$772.60