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	$116.80	6.631%	$124.545	$124.55	$124.55	$124.50
Purchase #2	$32.38	3.517%	$33.5188	$33.52	$33.50	$33.50
Purchase #3	$54.33	12.797%	$61.2826	$61.28	$61.30	$61.30
Purchase #4	$141.30	7.492%	$151.8862	$151.89	$151.90	$151.90
Purchase #5	$37.90	9.198%	$41.386	$41.39	$41.40	$41.40
Purchase #6	$122.72	4.587%	$128.3492	$128.35	$128.35	$128.30
Purchase #7	$93.77	13.687%	$106.6043	$106.60	$106.60	$106.60
7 purchase totals =	$599.20		$647.5721	$647.58	$647.60	$647.50