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	$139.82	10.529%	$154.5416	$154.54	$154.55	$154.50
Purchase #2	$12.32	11.189%	$13.6985	$13.70	$13.70	$13.70
Purchase #3	$244.92	8.451%	$265.6182	$265.62	$265.60	$265.60
Purchase #4	$223.71	13.174%	$253.1816	$253.18	$253.20	$253.20
Purchase #5	$90.50	10.618%	$100.1093	$100.11	$100.10	$100.10
Purchase #6	$187.40	6.648%	$199.8584	$199.86	$199.85	$199.90
Purchase #7	$112.71	3.206%	$116.3235	$116.32	$116.30	$116.30
7 purchase totals =	$1,011.38		$1,103.3311	$1,103.33	$1,103.30	$1,103.30