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	$15.78	7.254%	$16.9247	$16.92	$16.90	$16.90
Purchase #2	$137.27	6.519%	$146.2186	$146.22	$146.20	$146.20
Purchase #3	$36.97	10.635%	$40.9018	$40.90	$40.90	$40.90
Purchase #4	$59.42	3.150%	$61.2917	$61.29	$61.30	$61.30
Purchase #5	$14.51	5.225%	$15.2681	$15.27	$15.25	$15.30
Purchase #6	$249.75	7.619%	$268.7785	$268.78	$268.80	$268.80
Purchase #7	$20.56	4.605%	$21.5068	$21.51	$21.50	$21.50
7 purchase totals =	$534.26		$570.8902	$570.89	$570.85	$570.90