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	$27.68	12.441%	$31.1237	$31.12	$31.10	$31.10
Purchase #2	$126.98	10.685%	$140.5478	$140.55	$140.55	$140.50
Purchase #3	$57.88	12.447%	$65.0843	$65.08	$65.10	$65.10
Purchase #4	$127.62	3.736%	$132.3879	$132.39	$132.40	$132.40
Purchase #5	$70.78	11.274%	$78.7597	$78.76	$78.75	$78.80
Purchase #6	$114.42	11.696%	$127.8026	$127.80	$127.80	$127.80
Purchase #7	$214.88	8.111%	$232.3089	$232.31	$232.30	$232.30
7 purchase totals =	$740.24		$808.0149	$808.01	$808.00	$808.00