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	$209.73	12.789%	$236.5524	$236.55	$236.55	$236.60
Purchase #2	$156.73	9.225%	$171.1883	$171.19	$171.20	$171.20
Purchase #3	$84.37	6.220%	$89.6178	$89.62	$89.60	$89.60
Purchase #4	$224.79	13.744%	$255.6851	$255.69	$255.70	$255.70
Purchase #5	$94.95	11.133%	$105.5208	$105.52	$105.50	$105.50
Purchase #6	$110.51	7.760%	$119.0856	$119.09	$119.10	$119.10
Purchase #7	$39.35	9.433%	$43.0619	$43.06	$43.05	$43.10
7 purchase totals =	$920.43		$1,020.7119	$1,020.72	$1,020.70	$1,020.80