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	$46.97	7.533%	$50.5083	$50.51	$50.50	$50.50
Purchase #2	$221.46	5.249%	$233.0844	$233.08	$233.10	$233.10
Purchase #3	$195.81	12.774%	$220.8228	$220.82	$220.80	$220.80
Purchase #4	$160.67	4.794%	$168.3725	$168.37	$168.35	$168.40
Purchase #5	$98.71	11.287%	$109.8514	$109.85	$109.85	$109.90
Purchase #6	$122.87	13.823%	$139.8543	$139.85	$139.85	$139.90
Purchase #7	$191.32	7.303%	$205.2921	$205.29	$205.30	$205.30
7 purchase totals =	$1,037.81		$1,127.7858	$1,127.77	$1,127.75	$1,127.90