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	$240.59	5.103%	$252.8673	$252.87	$252.85	$252.90
Purchase #2	$192.54	7.126%	$206.2604	$206.26	$206.25	$206.30
Purchase #3	$207.94	10.638%	$230.0607	$230.06	$230.05	$230.10
Purchase #4	$38.67	4.244%	$40.3112	$40.31	$40.30	$40.30
Purchase #5	$33.86	10.745%	$37.4983	$37.50	$37.50	$37.50
Purchase #6	$196.33	13.740%	$223.3057	$223.31	$223.30	$223.30
Purchase #7	$59.46	12.625%	$66.9668	$66.97	$66.95	$67.00
7 purchase totals =	$969.39		$1,057.2704	$1,057.28	$1,057.20	$1,057.40