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	$59.65	6.298%	$63.4068	$63.41	$63.40	$63.40
Purchase #2	$227.33	5.160%	$239.0602	$239.06	$239.05	$239.10
Purchase #3	$222.99	8.759%	$242.5217	$242.52	$242.50	$242.50
Purchase #4	$101.39	13.272%	$114.8465	$114.85	$114.85	$114.80
Purchase #5	$59.59	3.205%	$61.4999	$61.50	$61.50	$61.50
Purchase #6	$79.52	12.144%	$89.1769	$89.18	$89.20	$89.20
Purchase #7	$165.71	11.699%	$185.0964	$185.10	$185.10	$185.10
7 purchase totals =	$916.18		$995.6084	$995.62	$995.60	$995.60