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	$10.81	12.392%	$12.1496	$12.15	$12.15	$12.10
Purchase #2	$65.54	3.518%	$67.8457	$67.85	$67.85	$67.80
Purchase #3	$87.99	9.792%	$96.606	$96.61	$96.60	$96.60
Purchase #4	$159.72	5.831%	$169.0333	$169.03	$169.05	$169.00
Purchase #5	$133.97	8.571%	$145.4526	$145.45	$145.45	$145.50
Purchase #6	$248.80	6.477%	$264.9148	$264.91	$264.90	$264.90
Purchase #7	$65.38	11.211%	$72.7098	$72.71	$72.70	$72.70
7 purchase totals =	$772.21		$828.7118	$828.71	$828.70	$828.60