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	$84.28	8.686%	$91.6006	$91.60	$91.60	$91.60
Purchase #2	$250.47	5.103%	$263.2515	$263.25	$263.25	$263.30
Purchase #3	$151.62	7.442%	$162.9036	$162.90	$162.90	$162.90
Purchase #4	$151.67	9.470%	$166.0331	$166.03	$166.05	$166.00
Purchase #5	$125.41	13.708%	$142.6012	$142.60	$142.60	$142.60
Purchase #6	$54.73	9.223%	$59.7777	$59.78	$59.80	$59.80
Purchase #7	$11.38	9.461%	$12.4567	$12.46	$12.45	$12.50
7 purchase totals =	$829.56		$898.6244	$898.62	$898.65	$898.70