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	$151.51	8.301%	$164.0868	$164.09	$164.10	$164.10
Purchase #2	$198.72	13.288%	$225.1259	$225.13	$225.15	$225.10
Purchase #3	$110.64	3.849%	$114.8985	$114.90	$114.90	$114.90
Purchase #4	$163.72	11.830%	$183.0881	$183.09	$183.10	$183.10
Purchase #5	$113.49	4.736%	$118.8649	$118.86	$118.85	$118.90
Purchase #6	$30.98	9.871%	$34.038	$34.04	$34.05	$34.00
Purchase #7	$68.54	5.651%	$72.4132	$72.41	$72.40	$72.40
7 purchase totals =	$837.60		$912.5154	$912.52	$912.55	$912.50