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	$160.42	10.444%	$177.1743	$177.17	$177.15	$177.20
Purchase #2	$103.33	7.826%	$111.4166	$111.42	$111.40	$111.40
Purchase #3	$39.55	10.305%	$43.6256	$43.63	$43.65	$43.60
Purchase #4	$126.69	11.845%	$141.6964	$141.70	$141.70	$141.70
Purchase #5	$158.95	7.839%	$171.4101	$171.41	$171.40	$171.40
Purchase #6	$27.59	12.789%	$31.1185	$31.12	$31.10	$31.10
Purchase #7	$123.31	12.813%	$139.1097	$139.11	$139.10	$139.10
7 purchase totals =	$739.84		$815.5512	$815.56	$815.50	$815.50