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	$69.30	7.472%	$74.4781	$74.48	$74.50	$74.50
Purchase #2	$112.45	3.322%	$116.1856	$116.19	$116.20	$116.20
Purchase #3	$56.26	9.480%	$61.5934	$61.59	$61.60	$61.60
Purchase #4	$104.36	6.396%	$111.0349	$111.03	$111.05	$111.00
Purchase #5	$55.25	12.526%	$62.1706	$62.17	$62.15	$62.20
Purchase #6	$37.78	9.450%	$41.3502	$41.35	$41.35	$41.40
Purchase #7	$24.72	10.301%	$27.2664	$27.27	$27.25	$27.30
7 purchase totals =	$460.12		$494.0792	$494.08	$494.10	$494.20