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	$27.71	6.692%	$29.5644	$29.56	$29.55	$29.60
Purchase #2	$227.73	5.606%	$240.4965	$240.50	$240.50	$240.50
Purchase #3	$190.48	7.664%	$205.0784	$205.08	$205.10	$205.10
Purchase #4	$49.63	7.297%	$53.2515	$53.25	$53.25	$53.30
Purchase #5	$229.78	9.105%	$250.7015	$250.70	$250.70	$250.70
Purchase #6	$70.34	11.614%	$78.5093	$78.51	$78.50	$78.50
Purchase #7	$248.83	6.550%	$265.1284	$265.13	$265.15	$265.10
7 purchase totals =	$1,044.50		$1,122.7300	$1,122.73	$1,122.75	$1,122.80