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	$208.38	13.283%	$236.0591	$236.06	$236.05	$236.10
Purchase #2	$123.74	13.238%	$140.1207	$140.12	$140.10	$140.10
Purchase #3	$200.30	7.581%	$215.4847	$215.48	$215.50	$215.50
Purchase #4	$106.39	5.856%	$112.6202	$112.62	$112.60	$112.60
Purchase #5	$169.27	8.336%	$183.3803	$183.38	$183.40	$183.40
Purchase #6	$55.77	10.750%	$61.7653	$61.77	$61.75	$61.80
Purchase #7	$120.90	5.276%	$127.2787	$127.28	$127.30	$127.30
7 purchase totals =	$984.75		$1,076.7090	$1,076.71	$1,076.70	$1,076.80