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	$87.38	9.577%	$95.7484	$95.75	$95.75	$95.70
Purchase #2	$50.82	13.410%	$57.635	$57.64	$57.65	$57.60
Purchase #3	$73.25	11.291%	$81.5207	$81.52	$81.50	$81.50
Purchase #4	$76.86	3.721%	$79.72	$79.72	$79.70	$79.70
Purchase #5	$109.64	13.185%	$124.096	$124.10	$124.10	$124.10
Purchase #6	$85.48	7.371%	$91.7807	$91.78	$91.80	$91.80
Purchase #7	$84.58	6.827%	$90.3543	$90.35	$90.35	$90.40
7 purchase totals =	$568.01		$620.8551	$620.86	$620.85	$620.80