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	$42.67	7.151%	$45.7213	$45.72	$45.70	$45.70
Purchase #2	$160.60	7.346%	$172.3977	$172.40	$172.40	$172.40
Purchase #3	$176.76	9.431%	$193.4302	$193.43	$193.45	$193.40
Purchase #4	$25.77	6.841%	$27.5329	$27.53	$27.55	$27.50
Purchase #5	$177.73	7.112%	$190.3702	$190.37	$190.35	$190.40
Purchase #6	$164.32	11.289%	$182.8701	$182.87	$182.85	$182.90
Purchase #7	$96.27	10.300%	$106.1858	$106.19	$106.20	$106.20
7 purchase totals =	$844.12		$918.5082	$918.51	$918.50	$918.50