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	$55.92	6.201%	$59.3876	$59.39	$59.40	$59.40
Purchase #2	$53.60	6.496%	$57.0819	$57.08	$57.10	$57.10
Purchase #3	$174.51	4.854%	$182.9807	$182.98	$183.00	$183.00
Purchase #4	$161.88	10.761%	$179.2999	$179.30	$179.30	$179.30
Purchase #5	$28.42	13.631%	$32.2939	$32.29	$32.30	$32.30
Purchase #6	$208.95	8.782%	$227.3	$227.30	$227.30	$227.30
Purchase #7	$105.95	9.697%	$116.224	$116.22	$116.20	$116.20
7 purchase totals =	$789.23		$854.5680	$854.56	$854.60	$854.60