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	$143.67	7.461%	$154.3892	$154.39	$154.40	$154.40
Purchase #2	$139.84	10.432%	$154.4281	$154.43	$154.45	$154.40
Purchase #3	$100.77	8.290%	$109.1238	$109.12	$109.10	$109.10
Purchase #4	$17.98	11.371%	$20.0245	$20.02	$20.00	$20.00
Purchase #5	$205.50	10.604%	$227.2912	$227.29	$227.30	$227.30
Purchase #6	$78.52	5.375%	$82.7405	$82.74	$82.75	$82.70
Purchase #7	$143.35	3.641%	$148.5694	$148.57	$148.55	$148.60
7 purchase totals =	$829.63		$896.5667	$896.56	$896.55	$896.50