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	$135.45	5.411%	$142.7792	$142.78	$142.80	$142.80
Purchase #2	$181.63	9.425%	$198.7486	$198.75	$198.75	$198.70
Purchase #3	$136.62	10.271%	$150.6522	$150.65	$150.65	$150.70
Purchase #4	$186.65	3.283%	$192.7777	$192.78	$192.80	$192.80
Purchase #5	$71.70	9.511%	$78.5194	$78.52	$78.50	$78.50
Purchase #6	$127.90	12.272%	$143.5959	$143.60	$143.60	$143.60
Purchase #7	$213.57	11.812%	$238.7969	$238.80	$238.80	$238.80
7 purchase totals =	$1,053.52		$1,145.8699	$1,145.88	$1,145.90	$1,145.90