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	$128.71	12.291%	$144.5297	$144.53	$144.55	$144.50
Purchase #2	$216.31	10.258%	$238.4991	$238.50	$238.50	$238.50
Purchase #3	$90.72	11.499%	$101.1519	$101.15	$101.15	$101.20
Purchase #4	$25.69	7.437%	$27.6006	$27.60	$27.60	$27.60
Purchase #5	$130.87	12.159%	$146.7825	$146.78	$146.80	$146.80
Purchase #6	$134.42	8.185%	$145.4223	$145.42	$145.40	$145.40
Purchase #7	$174.90	11.707%	$195.3755	$195.38	$195.40	$195.40
7 purchase totals =	$901.62		$999.3616	$999.36	$999.40	$999.40