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	$208.78	9.870%	$229.3866	$229.39	$229.40	$229.40
Purchase #2	$151.77	5.221%	$159.6939	$159.69	$159.70	$159.70
Purchase #3	$55.61	4.147%	$57.9161	$57.92	$57.90	$57.90
Purchase #4	$16.73	10.527%	$18.4912	$18.49	$18.50	$18.50
Purchase #5	$111.40	4.463%	$116.3718	$116.37	$116.35	$116.40
Purchase #6	$159.47	13.218%	$180.5487	$180.55	$180.55	$180.50
Purchase #7	$215.50	4.627%	$225.4712	$225.47	$225.45	$225.50
7 purchase totals =	$919.26		$987.8795	$987.88	$987.85	$987.90