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	$80.55	12.810%	$90.8685	$90.87	$90.85	$90.90
Purchase #2	$132.61	10.745%	$146.8589	$146.86	$146.85	$146.90
Purchase #3	$24.92	4.666%	$26.0828	$26.08	$26.10	$26.10
Purchase #4	$107.43	4.505%	$112.2697	$112.27	$112.25	$112.30
Purchase #5	$41.47	11.823%	$46.373	$46.37	$46.35	$46.40
Purchase #6	$116.94	3.184%	$120.6634	$120.66	$120.65	$120.70
Purchase #7	$6.59	8.411%	$7.1443	$7.14	$7.15	$7.10
7 purchase totals =	$510.51		$550.2606	$550.25	$550.20	$550.40