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	$74.61	4.626%	$78.0615	$78.06	$78.05	$78.10
Purchase #2	$66.66	6.373%	$70.9082	$70.91	$70.90	$70.90
Purchase #3	$175.42	13.315%	$198.7772	$198.78	$198.80	$198.80
Purchase #4	$43.91	10.285%	$48.4261	$48.43	$48.45	$48.40
Purchase #5	$37.26	4.472%	$38.9263	$38.93	$38.95	$38.90
Purchase #6	$134.42	10.750%	$148.8702	$148.87	$148.85	$148.90
Purchase #7	$5.75	8.428%	$6.2346	$6.23	$6.25	$6.20
7 purchase totals =	$538.03		$590.2041	$590.21	$590.25	$590.20