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	$250.36	10.862%	$277.5541	$277.55	$277.55	$277.60
Purchase #2	$174.72	5.366%	$184.0955	$184.10	$184.10	$184.10
Purchase #3	$171.36	13.296%	$194.144	$194.14	$194.15	$194.10
Purchase #4	$38.83	5.142%	$40.8266	$40.83	$40.85	$40.80
Purchase #5	$52.34	8.638%	$56.8611	$56.86	$56.85	$56.90
Purchase #6	$181.42	9.438%	$198.5424	$198.54	$198.55	$198.50
Purchase #7	$87.74	8.589%	$95.276	$95.28	$95.30	$95.30
7 purchase totals =	$956.77		$1,047.2997	$1,047.30	$1,047.35	$1,047.30