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	$13.56	6.316%	$14.4164	$14.42	$14.40	$14.40
Purchase #2	$175.56	13.273%	$198.8621	$198.86	$198.85	$198.90
Purchase #3	$114.67	11.844%	$128.2515	$128.25	$128.25	$128.30
Purchase #4	$75.46	7.461%	$81.0901	$81.09	$81.10	$81.10
Purchase #5	$109.73	12.508%	$123.455	$123.46	$123.45	$123.50
Purchase #6	$172.44	9.467%	$188.7649	$188.76	$188.75	$188.80
Purchase #7	$38.66	9.677%	$42.4011	$42.40	$42.40	$42.40
7 purchase totals =	$700.08		$777.2411	$777.24	$777.20	$777.40