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	$125.86	10.860%	$139.5284	$139.53	$139.55	$139.50
Purchase #2	$41.72	12.487%	$46.9296	$46.93	$46.95	$46.90
Purchase #3	$93.31	12.769%	$105.2248	$105.22	$105.20	$105.20
Purchase #4	$74.69	5.651%	$78.9107	$78.91	$78.90	$78.90
Purchase #5	$82.38	3.639%	$85.3778	$85.38	$85.40	$85.40
Purchase #6	$28.47	4.296%	$29.6931	$29.69	$29.70	$29.70
Purchase #7	$154.68	4.296%	$161.3251	$161.33	$161.35	$161.30
7 purchase totals =	$601.11		$646.9895	$646.99	$647.05	$646.90