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	$18.53	11.854%	$20.7265	$20.73	$20.75	$20.70
Purchase #2	$168.77	10.762%	$186.933	$186.93	$186.95	$186.90
Purchase #3	$176.87	6.221%	$187.8731	$187.87	$187.85	$187.90
Purchase #4	$51.63	11.444%	$57.5385	$57.54	$57.55	$57.50
Purchase #5	$174.29	4.196%	$181.6032	$181.60	$181.60	$181.60
Purchase #6	$241.49	8.355%	$261.6665	$261.67	$261.65	$261.70
Purchase #7	$99.65	11.665%	$111.2742	$111.27	$111.25	$111.30
7 purchase totals =	$931.23		$1,007.6150	$1,007.61	$1,007.60	$1,007.60