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	$81.64	10.622%	$90.3118	$90.31	$90.30	$90.30
Purchase #2	$192.96	9.145%	$210.6062	$210.61	$210.60	$210.60
Purchase #3	$71.73	13.515%	$81.4243	$81.42	$81.40	$81.40
Purchase #4	$50.82	7.631%	$54.6981	$54.70	$54.70	$54.70
Purchase #5	$242.59	8.796%	$263.9282	$263.93	$263.95	$263.90
Purchase #6	$180.68	5.447%	$190.5216	$190.52	$190.50	$190.50
Purchase #7	$69.53	3.645%	$72.0644	$72.06	$72.05	$72.10
7 purchase totals =	$889.95		$963.5546	$963.55	$963.50	$963.50