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	$242.77	6.650%	$258.9142	$258.91	$258.90	$258.90
Purchase #2	$143.40	3.797%	$148.8449	$148.84	$148.85	$148.80
Purchase #3	$54.40	5.872%	$57.5944	$57.59	$57.60	$57.60
Purchase #4	$11.98	5.592%	$12.6499	$12.65	$12.65	$12.60
Purchase #5	$52.31	8.807%	$56.9169	$56.92	$56.90	$56.90
Purchase #6	$89.26	10.271%	$98.4279	$98.43	$98.45	$98.40
Purchase #7	$250.39	6.835%	$267.5042	$267.50	$267.50	$267.50
7 purchase totals =	$844.51		$900.8524	$900.84	$900.85	$900.70