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	$126.37	9.820%	$138.7795	$138.78	$138.80	$138.80
Purchase #2	$207.93	11.865%	$232.6009	$232.60	$232.60	$232.60
Purchase #3	$71.62	12.109%	$80.2925	$80.29	$80.30	$80.30
Purchase #4	$51.54	8.365%	$55.8513	$55.85	$55.85	$55.90
Purchase #5	$250.89	13.813%	$285.5454	$285.55	$285.55	$285.50
Purchase #6	$203.94	5.660%	$215.483	$215.48	$215.50	$215.50
Purchase #7	$55.61	10.268%	$61.32	$61.32	$61.30	$61.30
7 purchase totals =	$967.90		$1,069.8726	$1,069.87	$1,069.90	$1,069.90