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	$122.90	3.832%	$127.6095	$127.61	$127.60	$127.60
Purchase #2	$183.49	11.197%	$204.0354	$204.04	$204.05	$204.00
Purchase #3	$53.73	7.285%	$57.6442	$57.64	$57.65	$57.60
Purchase #4	$20.73	5.742%	$21.9203	$21.92	$21.90	$21.90
Purchase #5	$193.91	9.134%	$211.6217	$211.62	$211.60	$211.60
Purchase #6	$50.57	7.235%	$54.2287	$54.23	$54.25	$54.20
Purchase #7	$245.96	12.398%	$276.4541	$276.45	$276.45	$276.50
7 purchase totals =	$871.29		$953.5139	$953.51	$953.50	$953.40