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	$53.62	13.222%	$60.7096	$60.71	$60.70	$60.70
Purchase #2	$196.50	12.769%	$221.5911	$221.59	$221.60	$221.60
Purchase #3	$134.96	3.211%	$139.2936	$139.29	$139.30	$139.30
Purchase #4	$65.46	7.611%	$70.4422	$70.44	$70.45	$70.40
Purchase #5	$199.48	9.301%	$218.0336	$218.03	$218.05	$218.00
Purchase #6	$112.82	13.371%	$127.9052	$127.91	$127.90	$127.90
Purchase #7	$233.90	11.633%	$261.1096	$261.11	$261.10	$261.10
7 purchase totals =	$996.74		$1,099.0849	$1,099.08	$1,099.10	$1,099.00