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	$20.90	12.274%	$23.4653	$23.47	$23.45	$23.50
Purchase #2	$156.78	9.360%	$171.4546	$171.45	$171.45	$171.50
Purchase #3	$169.99	12.849%	$191.832	$191.83	$191.85	$191.80
Purchase #4	$56.72	12.704%	$63.9257	$63.93	$63.95	$63.90
Purchase #5	$39.32	5.697%	$41.5601	$41.56	$41.55	$41.60
Purchase #6	$99.48	12.343%	$111.7588	$111.76	$111.75	$111.80
Purchase #7	$14.46	3.121%	$14.9113	$14.91	$14.90	$14.90
7 purchase totals =	$557.65		$618.9078	$618.91	$618.90	$619.00