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	$162.93	5.283%	$171.5376	$171.54	$171.55	$171.50
Purchase #2	$217.26	10.708%	$240.5242	$240.52	$240.50	$240.50
Purchase #3	$140.98	10.251%	$155.4319	$155.43	$155.45	$155.40
Purchase #4	$56.72	6.366%	$60.3308	$60.33	$60.35	$60.30
Purchase #5	$50.61	10.225%	$55.7849	$55.78	$55.80	$55.80
Purchase #6	$25.71	7.249%	$27.5737	$27.57	$27.55	$27.60
Purchase #7	$133.27	9.212%	$145.5468	$145.55	$145.55	$145.50
7 purchase totals =	$787.48		$856.7299	$856.72	$856.75	$856.60