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	$157.75	13.228%	$178.6172	$178.62	$178.60	$178.60
Purchase #2	$218.92	12.407%	$246.0814	$246.08	$246.10	$246.10
Purchase #3	$126.39	12.819%	$142.5919	$142.59	$142.60	$142.60
Purchase #4	$122.46	11.475%	$136.5123	$136.51	$136.50	$136.50
Purchase #5	$157.91	6.105%	$167.5504	$167.55	$167.55	$167.60
Purchase #6	$122.43	4.445%	$127.872	$127.87	$127.85	$127.90
Purchase #7	$191.48	4.746%	$200.5676	$200.57	$200.55	$200.60
7 purchase totals =	$1,097.34		$1,199.7928	$1,199.79	$1,199.75	$1,199.90