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	$123.80	10.291%	$136.5403	$136.54	$136.55	$136.50
Purchase #2	$212.68	10.152%	$234.2713	$234.27	$234.25	$234.30
Purchase #3	$225.54	10.606%	$249.4608	$249.46	$249.45	$249.50
Purchase #4	$55.84	10.776%	$61.8573	$61.86	$61.85	$61.90
Purchase #5	$43.96	5.485%	$46.3712	$46.37	$46.35	$46.40
Purchase #6	$78.55	4.838%	$82.3502	$82.35	$82.35	$82.40
Purchase #7	$64.49	10.118%	$71.0151	$71.02	$71.00	$71.00
7 purchase totals =	$804.86		$881.8662	$881.87	$881.80	$882.00