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	$249.58	11.617%	$278.5737	$278.57	$278.55	$278.60
Purchase #2	$50.63	6.277%	$53.808	$53.81	$53.80	$53.80
Purchase #3	$22.97	5.376%	$24.2049	$24.20	$24.20	$24.20
Purchase #4	$219.27	8.240%	$237.3378	$237.34	$237.35	$237.30
Purchase #5	$56.80	5.453%	$59.8973	$59.90	$59.90	$59.90
Purchase #6	$41.92	13.557%	$47.6031	$47.60	$47.60	$47.60
Purchase #7	$36.67	10.329%	$40.4576	$40.46	$40.45	$40.50
7 purchase totals =	$677.84		$741.8824	$741.88	$741.85	$741.90