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	$183.41	11.506%	$204.5132	$204.51	$204.50	$204.50
Purchase #2	$234.37	3.225%	$241.9284	$241.93	$241.95	$241.90
Purchase #3	$135.78	4.144%	$141.4067	$141.41	$141.40	$141.40
Purchase #4	$78.68	13.231%	$89.0902	$89.09	$89.10	$89.10
Purchase #5	$223.59	5.679%	$236.2877	$236.29	$236.30	$236.30
Purchase #6	$95.96	12.325%	$107.7871	$107.79	$107.80	$107.80
Purchase #7	$99.27	12.329%	$111.509	$111.51	$111.50	$111.50
7 purchase totals =	$1,051.06		$1,132.5223	$1,132.53	$1,132.55	$1,132.50