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	$19.82	3.442%	$20.5022	$20.50	$20.50	$20.50
Purchase #2	$106.32	4.466%	$111.0683	$111.07	$111.05	$111.10
Purchase #3	$229.38	7.645%	$246.9161	$246.92	$246.90	$246.90
Purchase #4	$227.57	7.705%	$245.1043	$245.10	$245.10	$245.10
Purchase #5	$12.69	7.406%	$13.6298	$13.63	$13.65	$13.60
Purchase #6	$153.85	3.243%	$158.8394	$158.84	$158.85	$158.80
Purchase #7	$165.39	11.694%	$184.7307	$184.73	$184.75	$184.70
7 purchase totals =	$915.02		$980.7908	$980.79	$980.80	$980.70