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	$54.74	5.586%	$57.7978	$57.80	$57.80	$57.80
Purchase #2	$177.35	3.597%	$183.7293	$183.73	$183.75	$183.70
Purchase #3	$34.93	7.129%	$37.4202	$37.42	$37.40	$37.40
Purchase #4	$179.46	11.151%	$199.4716	$199.47	$199.45	$199.50
Purchase #5	$232.54	12.503%	$261.6145	$261.61	$261.60	$261.60
Purchase #6	$69.61	12.601%	$78.3816	$78.38	$78.40	$78.40
Purchase #7	$195.51	10.295%	$215.6378	$215.64	$215.65	$215.60
7 purchase totals =	$944.14		$1,034.0528	$1,034.05	$1,034.05	$1,034.00