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	$109.91	11.435%	$122.4782	$122.48	$122.50	$122.50
Purchase #2	$146.94	12.626%	$165.4926	$165.49	$165.50	$165.50
Purchase #3	$198.41	13.265%	$224.7291	$224.73	$224.75	$224.70
Purchase #4	$163.43	3.874%	$169.7613	$169.76	$169.75	$169.80
Purchase #5	$83.55	8.393%	$90.5624	$90.56	$90.55	$90.60
Purchase #6	$59.93	5.191%	$63.041	$63.04	$63.05	$63.00
Purchase #7	$166.92	9.865%	$183.3867	$183.39	$183.40	$183.40
7 purchase totals =	$929.09		$1,019.4513	$1,019.45	$1,019.50	$1,019.50