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	$244.42	13.156%	$276.5759	$276.58	$276.60	$276.60
Purchase #2	$197.52	10.535%	$218.3287	$218.33	$218.35	$218.30
Purchase #3	$190.31	9.326%	$208.0583	$208.06	$208.05	$208.10
Purchase #4	$82.44	4.113%	$85.8308	$85.83	$85.85	$85.80
Purchase #5	$16.67	5.171%	$17.532	$17.53	$17.55	$17.50
Purchase #6	$59.50	3.760%	$61.7372	$61.74	$61.75	$61.70
Purchase #7	$56.33	9.151%	$61.4848	$61.48	$61.50	$61.50
7 purchase totals =	$847.19		$929.5477	$929.55	$929.65	$929.50