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	$40.32	5.557%	$42.5606	$42.56	$42.55	$42.60
Purchase #2	$192.36	9.531%	$210.6938	$210.69	$210.70	$210.70
Purchase #3	$248.74	10.613%	$275.1388	$275.14	$275.15	$275.10
Purchase #4	$182.86	7.412%	$196.4136	$196.41	$196.40	$196.40
Purchase #5	$12.76	5.382%	$13.4467	$13.45	$13.45	$13.40
Purchase #6	$49.42	7.340%	$53.0474	$53.05	$53.05	$53.00
Purchase #7	$38.40	11.201%	$42.7012	$42.70	$42.70	$42.70
7 purchase totals =	$764.86		$834.0021	$834.00	$834.00	$833.90