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	$45.50	7.427%	$48.8793	$48.88	$48.90	$48.90
Purchase #2	$249.39	10.179%	$274.7754	$274.78	$274.80	$274.80
Purchase #3	$245.55	8.401%	$266.1787	$266.18	$266.20	$266.20
Purchase #4	$76.92	7.141%	$82.4129	$82.41	$82.40	$82.40
Purchase #5	$80.38	3.320%	$83.0486	$83.05	$83.05	$83.00
Purchase #6	$215.87	4.863%	$226.3678	$226.37	$226.35	$226.40
Purchase #7	$78.46	5.104%	$82.4646	$82.46	$82.45	$82.50
7 purchase totals =	$992.07		$1,064.1273	$1,064.13	$1,064.15	$1,064.20