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	$118.40	13.785%	$134.7214	$134.72	$134.70	$134.70
Purchase #2	$85.79	4.618%	$89.7518	$89.75	$89.75	$89.80
Purchase #3	$144.91	13.821%	$164.938	$164.94	$164.95	$164.90
Purchase #4	$9.33	7.278%	$10.009	$10.01	$10.00	$10.00
Purchase #5	$63.55	10.671%	$70.3314	$70.33	$70.35	$70.30
Purchase #6	$223.81	4.732%	$234.4007	$234.40	$234.40	$234.40
Purchase #7	$163.35	13.758%	$185.8237	$185.82	$185.80	$185.80
7 purchase totals =	$809.14		$889.9760	$889.97	$889.95	$889.90