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	$159.91	7.105%	$171.2716	$171.27	$171.25	$171.30
Purchase #2	$176.51	4.856%	$185.0813	$185.08	$185.10	$185.10
Purchase #3	$226.38	6.185%	$240.3816	$240.38	$240.40	$240.40
Purchase #4	$101.85	4.851%	$106.7907	$106.79	$106.80	$106.80
Purchase #5	$34.91	13.127%	$39.4926	$39.49	$39.50	$39.50
Purchase #6	$197.33	6.390%	$209.9394	$209.94	$209.95	$209.90
Purchase #7	$19.26	4.262%	$20.0809	$20.08	$20.10	$20.10
7 purchase totals =	$916.15		$973.0381	$973.03	$973.10	$973.10