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	$128.81	9.675%	$141.2724	$141.27	$141.25	$141.30
Purchase #2	$93.96	11.427%	$104.6968	$104.70	$104.70	$104.70
Purchase #3	$102.63	13.537%	$116.523	$116.52	$116.50	$116.50
Purchase #4	$144.63	4.574%	$151.2454	$151.25	$151.25	$151.20
Purchase #5	$86.44	4.523%	$90.3497	$90.35	$90.35	$90.30
Purchase #6	$17.42	8.690%	$18.9338	$18.93	$18.95	$18.90
Purchase #7	$186.50	13.596%	$211.8565	$211.86	$211.85	$211.90
7 purchase totals =	$760.39		$834.8776	$834.88	$834.85	$834.80