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	$30.37	10.829%	$33.6588	$33.66	$33.65	$33.70
Purchase #2	$227.39	10.114%	$250.3882	$250.39	$250.40	$250.40
Purchase #3	$37.49	3.446%	$38.7819	$38.78	$38.80	$38.80
Purchase #4	$248.35	10.739%	$275.0203	$275.02	$275.00	$275.00
Purchase #5	$240.80	6.433%	$256.2907	$256.29	$256.30	$256.30
Purchase #6	$17.71	13.151%	$20.039	$20.04	$20.05	$20.00
Purchase #7	$46.82	10.734%	$51.8457	$51.85	$51.85	$51.80
7 purchase totals =	$848.93		$926.0246	$926.03	$926.05	$926.00