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	$36.44	8.295%	$39.4627	$39.46	$39.45	$39.50
Purchase #2	$34.54	9.523%	$37.8292	$37.83	$37.85	$37.80
Purchase #3	$159.51	6.373%	$169.6756	$169.68	$169.70	$169.70
Purchase #4	$98.50	6.757%	$105.1556	$105.16	$105.15	$105.20
Purchase #5	$200.61	4.589%	$209.816	$209.82	$209.80	$209.80
Purchase #6	$162.52	12.834%	$183.3778	$183.38	$183.40	$183.40
Purchase #7	$102.59	11.512%	$114.4002	$114.40	$114.40	$114.40
7 purchase totals =	$794.71		$859.7171	$859.73	$859.75	$859.80