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	$240.94	6.343%	$256.2228	$256.22	$256.20	$256.20
Purchase #2	$239.90	11.479%	$267.4381	$267.44	$267.45	$267.40
Purchase #3	$51.54	9.623%	$56.4997	$56.50	$56.50	$56.50
Purchase #4	$181.47	4.179%	$189.0536	$189.05	$189.05	$189.10
Purchase #5	$155.97	7.597%	$167.819	$167.82	$167.80	$167.80
Purchase #6	$88.97	11.859%	$99.521	$99.52	$99.50	$99.50
Purchase #7	$62.32	5.105%	$65.5014	$65.50	$65.50	$65.50
7 purchase totals =	$1,021.11		$1,102.0556	$1,102.05	$1,102.00	$1,102.00