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	$44.50	13.163%	$50.3575	$50.36	$50.35	$50.40
Purchase #2	$39.54	4.118%	$41.1683	$41.17	$41.15	$41.20
Purchase #3	$179.83	3.263%	$185.6979	$185.70	$185.70	$185.70
Purchase #4	$192.80	11.865%	$215.6757	$215.68	$215.70	$215.70
Purchase #5	$126.43	10.154%	$139.2677	$139.27	$139.25	$139.30
Purchase #6	$226.56	12.793%	$255.5438	$255.54	$255.55	$255.50
Purchase #7	$79.76	13.129%	$90.2317	$90.23	$90.25	$90.20
7 purchase totals =	$889.42		$977.9426	$977.95	$977.95	$978.00