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	$83.43	8.327%	$90.3772	$90.38	$90.40	$90.40
Purchase #2	$142.92	5.336%	$150.5462	$150.55	$150.55	$150.50
Purchase #3	$102.59	5.166%	$107.8898	$107.89	$107.90	$107.90
Purchase #4	$138.88	11.637%	$155.0415	$155.04	$155.05	$155.00
Purchase #5	$235.69	9.810%	$258.8112	$258.81	$258.80	$258.80
Purchase #6	$108.79	3.760%	$112.8805	$112.88	$112.90	$112.90
Purchase #7	$68.39	10.345%	$75.4649	$75.46	$75.45	$75.50
7 purchase totals =	$880.69		$951.0113	$951.01	$951.05	$951.00