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	$166.28	12.195%	$186.5578	$186.56	$186.55	$186.60
Purchase #2	$197.85	3.789%	$205.3465	$205.35	$205.35	$205.30
Purchase #3	$116.83	8.331%	$126.5631	$126.56	$126.55	$126.60
Purchase #4	$54.69	12.313%	$61.424	$61.42	$61.40	$61.40
Purchase #5	$65.71	11.176%	$73.0537	$73.05	$73.05	$73.10
Purchase #6	$46.70	3.859%	$48.5022	$48.50	$48.50	$48.50
Purchase #7	$114.95	7.399%	$123.4552	$123.46	$123.45	$123.50
7 purchase totals =	$763.01		$824.9025	$824.90	$824.85	$825.00