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	$236.96	9.786%	$260.1489	$260.15	$260.15	$260.10
Purchase #2	$50.90	6.855%	$54.3892	$54.39	$54.40	$54.40
Purchase #3	$69.47	13.775%	$79.0395	$79.04	$79.05	$79.00
Purchase #4	$79.70	8.381%	$86.3797	$86.38	$86.40	$86.40
Purchase #5	$171.42	5.442%	$180.7487	$180.75	$180.75	$180.70
Purchase #6	$146.39	3.243%	$151.1374	$151.14	$151.15	$151.10
Purchase #7	$71.94	9.119%	$78.5002	$78.50	$78.50	$78.50
7 purchase totals =	$826.78		$890.3436	$890.35	$890.40	$890.20