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	$86.89	13.388%	$98.5228	$98.52	$98.50	$98.50
Purchase #2	$71.32	10.856%	$79.0625	$79.06	$79.05	$79.10
Purchase #3	$250.97	13.221%	$284.1507	$284.15	$284.15	$284.20
Purchase #4	$7.30	6.187%	$7.7517	$7.75	$7.75	$7.80
Purchase #5	$113.52	13.273%	$128.5875	$128.59	$128.60	$128.60
Purchase #6	$81.35	10.669%	$90.0292	$90.03	$90.05	$90.00
Purchase #7	$89.47	9.392%	$97.873	$97.87	$97.85	$97.90
7 purchase totals =	$700.82		$785.9774	$785.97	$785.95	$786.10