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	$94.28	6.469%	$100.379	$100.38	$100.40	$100.40
Purchase #2	$207.50	7.335%	$222.7201	$222.72	$222.70	$222.70
Purchase #3	$146.47	5.501%	$154.5273	$154.53	$154.55	$154.50
Purchase #4	$155.51	6.228%	$165.1952	$165.20	$165.20	$165.20
Purchase #5	$245.93	13.212%	$278.4223	$278.42	$278.40	$278.40
Purchase #6	$138.35	13.213%	$156.6302	$156.63	$156.65	$156.60
Purchase #7	$62.30	7.449%	$66.9407	$66.94	$66.95	$66.90
7 purchase totals =	$1,050.34		$1,144.8148	$1,144.82	$1,144.85	$1,144.70