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	$250.54	10.420%	$276.6463	$276.65	$276.65	$276.60
Purchase #2	$62.88	12.190%	$70.5451	$70.55	$70.55	$70.50
Purchase #3	$212.69	7.610%	$228.8757	$228.88	$228.90	$228.90
Purchase #4	$245.63	3.717%	$254.7601	$254.76	$254.75	$254.80
Purchase #5	$126.61	13.464%	$143.6568	$143.66	$143.65	$143.70
Purchase #6	$119.74	6.311%	$127.2968	$127.30	$127.30	$127.30
Purchase #7	$77.80	7.716%	$83.803	$83.80	$83.80	$83.80
7 purchase totals =	$1,095.89		$1,185.5838	$1,185.60	$1,185.60	$1,185.60