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	$14.31	10.746%	$15.8478	$15.85	$15.85	$15.80
Purchase #2	$134.27	9.155%	$146.5624	$146.56	$146.55	$146.60
Purchase #3	$102.52	4.608%	$107.2441	$107.24	$107.25	$107.20
Purchase #4	$177.89	6.477%	$189.4119	$189.41	$189.40	$189.40
Purchase #5	$195.55	11.780%	$218.5858	$218.59	$218.60	$218.60
Purchase #6	$161.54	9.806%	$177.3806	$177.38	$177.40	$177.40
Purchase #7	$98.25	13.444%	$111.4587	$111.46	$111.45	$111.50
7 purchase totals =	$884.33		$966.4913	$966.49	$966.50	$966.50