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	$52.89	8.434%	$57.3507	$57.35	$57.35	$57.40
Purchase #2	$103.80	3.815%	$107.76	$107.76	$107.75	$107.80
Purchase #3	$140.26	13.720%	$159.5037	$159.50	$159.50	$159.50
Purchase #4	$43.82	12.404%	$49.2554	$49.26	$49.25	$49.30
Purchase #5	$100.61	3.720%	$104.3527	$104.35	$104.35	$104.40
Purchase #6	$64.86	11.466%	$72.2968	$72.30	$72.30	$72.30
Purchase #7	$101.99	12.553%	$114.7928	$114.79	$114.80	$114.80
7 purchase totals =	$608.23		$665.3121	$665.31	$665.30	$665.50